Look at how much cores the processor has more cores means more power, but 8 cores of 1.6GHz is as good as 4 cores 3.2GHz so be careful with that. Also the CPU has to fit the Motherboard slot. The computer also needs RAM also known as Work Memory and you have to be careful because you have 4 RAM slot types DDR1, DDR2, DDR3 and the newest is DDR4 but DDR1 and DDR2 are outdated so you can't find motherboards with those slot types, also you have to do research in how much MHz your motherboard can handle DDR3 MHz minimum is 1600MHz and DDR4 MHz minimum is 2133 MHz so you should buy RAM sticks with atleast 1600MHz for DDR3 and atleast 2133MHz for DDR4. As of the graphics card the graphics card can fit almost every motherboard with PCI-E 3 slot the only exception is when it doesn't fit the computer case :(. Graphics cards are simpler so you can just do a little research in that. The motherboard doesn't really matter only thing that matters is the DDR slot you are gonna use for the RAM. In short more GHz or MHz is better, as for how much RAM you're gonna need depends. Normal PC 8gb. Gaming PC 16gb(can be used for normal photo editing). And for Hardcore Video/Photo editing 32/64GB depends how much you need. You can also use PC Part Picker
https://www.pcpartpicker.com like @
ThatGuyYouDespise suggested.