Start by doing lots of research! Google, Google, Google!!!
Then pick the chipset/ram for your budget (newest isn't always the best)
Keep in mind.., if you go older, you usually need more power...
If you want high end graphics... you need high end power... (usually modular) then you can change more later without having to upgrade power,
Don't buy a shitty motherboard!!!
If you start with a good mobo and power supply, it's much easier to upgrade later...
Experiment!
If you buy the wrong stuff and it doesn't work out... sell it for much, much less, cut your losses,,, and start again
Good luck And may the PC Building Force be with you my young Padawan!!