So im about to start building my first custom gaming PC but I watched a video on installing drivers (motherboard driver, and graphics card driver) and it made me wonder do I have to install them.
At minimum you need to install your network driver. No internet means no automatic driver updates. You should go to the motherboard manufacturers website and grab all the latest drivers for your system.
If the question is do I need them at all, yes, no drivers=no use.