Welcome to the forum. I used Google Translate. Here's part of what I came up with: "I dispose of fixed elements that I have previously drawn as pieces, but when making an assembly apart from those predefined as pieces elements is necessary to design others that depend partly on these, but I feel limited when it comes to design them in assembly and there are 3D design options that are not included within the assembly function."
You can use top down design in SolidWorks, but you can't add material directly in an assembly function. You'll either need to edit an existing Part within the Assembly, or create a virtual Part inside the Assembly.