@anarceus here's a guide that goes a bit more in detail https://www.techradar.com/how-to/how-to-build-a-pc
your parts, especially your motherboard and your case should also come with written documentation that should inform you about the specifics, like which PCIe slots can be used at the same time
@noiob thanks! Yeah it does, PCIe is next I think, only things missing are the graphics card and the PSU (and the remaining cooler wiring)