As a disclaimer, I don't pretend to be any kind of hardware expert, so the information I give here will be mostly a compilation of stuff I've picked up reading posts on the forum. Now that I have that out of the way, the answer to what kind of computer you need will depend on your specific use. If you do a lot of rendering I understand that can affect the answer. For most operations SW uses a single core, although I believe that might not be the case for simulation (see the Reply from Nick Birkett-Smith at New Computer for Solidworks question: 1 Processor with 12 Core or 2 processors with 4 core each), so if you're just doing basic modeling and Drawings you won't get much benefit from multiple cores. What IS the Best CPU for SOLIDWORKS? and https://www.javelin-tech.com/blog/2019/10/solidworks-2020-hardware-recommendations/ are other sites you might want to check out.
Don't get a gaming video card. While some people use them without major problems, many aren't that lucky, and I seem to see a lot of posts from people who were using one and an automatic driver update made them completely unusable for Solidworks. Get a video card (and driver for it) that's recommended by Solidworks.
When you get a preliminary selection, go to this site to evaluate it, and then I'd encourage you to contact your VAR (Value Added Reseller; the company you bought Solidworks from) and get their input. Be sure to tell them what kind of work you'll be doing. I'm pretty sure they'd rather help you select a machine that works well now instead of getting calls asking for help when you get a bad one.
If you're a student, or off subscription, and therefore can't ask a VAR, the site I posted above should help, or do a search in the Discussion section of this forum (Boxx Apexx OR Dell Precision? posted by Rob Edwards would be a good place to start, or Buying New CAD Workstations or Computer for Solidworks 2018, or do a search for posts by Charles Culp, who has given some excellent advice to many people, including me, although he hasn't been around the forum much lately). If a search doesn't help feel free to post your specs there in a new Discussion. I'm sure someone will be glad to give you some input.
I'm not going to recommend any specific brands, but while I've always used Dell, and have had good luck with them, I've heard many good things about Boxx (Custom Workstations for Your High Performance Computing Needs | BOXX) and SolidBox (https://www.mysolidbox.com/). It's my understanding that they will optimize a computer for use with Solidworks. If I was buying my own instead of my employer providing it I'd probably look into getting one from one of those companies.
If you're thinking about a Mac I'd encourage you to reconsider. If you really want one (or already have one), and only need SolidWorks for a class or occasional use, see 2019-20 Student Edition on a Mac, and maybe the post from Anna Wood at what is the best way to run SW on a Mac laptop?.
I'm attaching the specs for my computer. Again, I'm not advocating for any brand, but this one works well for me (and I did have the helpful people at GoEngineer review the specs for me before getting it). I work with Parts, Assemblies, and Drawings, but I don't do any Simulation or Rendering, so I can't promise a similar machine will work well for you. (2020-04-19 edit: I'm attaching the specs for my new computer, but I'll leave the previous one. So far the new one is working well also.)
Edit: I saw the information below posted by Mathieu Myrand-Bolduc in a Reply on the Discussion section of this forum, and he graciously agreed to let me quote it here. There's some good stuff in it.
"The place I work at does a lot of things through the API, some of it takes a lot of time, up to several hours actually, so we looked into a lot into the performance question, plus like @Jeff Mowry I like to game, so we went for what amounts to a high power gaming rig with a Quadro/Firepro video card. But in the process, we learned a lot about how Solidworks uses the hardware. The following is a resume of what we discovered. It was evaluated on SW 2016 and we mostly evaluated Intel/NVIDIA hardware. The conclusions "should" hold true for AMD hardware. Please note that we are running 3K components + sheet metal assemblies, so this should be a rather high end machine.
Assembly/rebuilds/Part creation: Uses a single core. If what you mostly do is Part and assembly creation, go for a High clock speed cpu. Note that more recent are usually a bit more powerful (a few % points). We went for a intel I-7 6700K. Theoretically you could go for a I-5 if you wanted to save some money, since the major difference is the hyper-threading and you have other cores that are free, so it shouldn't slow you down too much. Xeon were not evaluated, since the cost for high speed cpu was ridiculous and we didn't feel their differences added anything to us. Besides we had enough of our 2 core 2.5 ghz machines .....
Drawings: This is a bit different, since the view regeneration uses multiple cores. If you don't have to rebuild the assemblies, then go for a bigger core count. You want a high clock speed too for the odd time when you must rebuild. We didn't test this specifically, but that's what came up on several resources .
Rendering, FEA: We didn't test, but unless Solidworks did something weird these operations should be able to use multiple cores, so my guess would be a high core count. I would guess the new I-9 would shine there.
All operations: As much as needed. If you are working with small to medium assemblies and not opening anything ram heavy, then 16 gb should be enough. We went for 32 gb thought and I personally saw solidworks eat 22 gb on a single assembly (yes I opened it in resolved mode ....). Most recent high end cpu can go up to 64 gb, maybe 128 gb (probably an overkill). I have seen a benchmark suggesting that ram speed does not matter much on gaming performance, so I wouldn't worry about that too much.
Get a pro card, Quadro/Firepro. You can use a gaming card, but you loose a lot of performance and get weird results. I tested this at home (I have a Geforce 970) and It was a lot slower and less stable than what I had at work. I will admit that I didn't test without the registry key hack to enable real view and the other advanced options. I noted that the shaded with edge option was particularly slow on my machine. I suspect that there is special hardware in the Quadro/Firepro gpus. We have mid range Quadros and it works fine for medium/big assemblies. It is used mostly when you play with the views (rotation, move, display state changes , etc...).
As fast as possible. This affects everything, from boot time to opening Solidworks to opening and saving of files (on the hard disk of course). I would recommend the new M.2 hard disks, check the benchmarks, some are truly better. We have Samsung EVO 850, but the new ones are a lot faster.
Final notes on overclocking the CPU. CPU clock speed and performance are just about linear, so double the speed and you should just about cut the time in half. However, unless you spend a LOT of time in an intensive CPU operation, the gains in a day won't be that impressive for a user. Especially since you won't do more than a 30% clock speed increase (we did 15% I think). If you buy an OC box, sure, they tested it and are giving you a warranty on it, but if you want to do it yourself, unless it's for fun, I would leave it stock (or maybe boost all cores to turbo speed), or be ready to spend some time testing stability. We did it, because we are doing CPU intensive stuff, but you have to be careful, Solidworks can become unstable even if your system looks rock steady."