1) Why after I finished a sketch I cannot extrude it because all solid and extrude functions are grayed out?

Is this a bug? Do I need to re-install Solidworks?

2) If I made a surface and I want to completely fill it and torn it into a solid with no cavities inside, how do I achieve that?

3) I was designing this part for a toy microscope and I tried to center a screw hole on this round part. When I got my ability to place objects on a sketch, I lost my ability to place holes...

4) Is it possible to overlap two objects and get a third object out of where those two objects intersect, just like in Autodesk Inventor Pro?

(autodesk inventor offers boolian AND, OR, NOT to be done with solids)

5) Why when I go to the settings menu, I can see all command tabs that I want, but when I exit the menu, no matter what options I choose, I am only left with few basic command tabs? Is this a bug? Sometimes I cannot follow youtube videos on how to do things because I dont have those tabs handy to me.

Thank you.