usually you only have to BE SURE of just a few things:
1. Will this Motherboard support this RAM and Processor
2. Will this PSU handle the voltage, INCLUDING having the right plugs for my motherboard AND video card
3. Is this motherboard physically going to FIT into the case (including having the correct screw pattern, e.g. ATX, mATX, BTX, etc.), and is this video card going to physically FIT after everything is installed
4. this one has become more prevalent lately: Will my CPU cooler FIT without interfering with cables, case side-door, etc.
covering those, is about 95% of custom building a PC (there are exceptions of course)