BUPC Memory aka RAM
Select Memory Module aka RAM for Your PC.
Most of The Latest Motherboards Use DDR4 type of memory. Motherboards that use DDR4 Memory Modules, have the keyword "DDR4" in their name (or in Description) so that you can easily figure out if motherboard will use DDR4 or not.
Most Brands are Fine, Select as per your budget. As a rule of thumb, More GB The Better it is. Higher The Speed (Clock Speed i.e., 1600mhz. or 2133mhz.) will make PC perform better, faster. Performance PC's like for Gaming or Designing better do with Memories with Heat Sink (Name with keywords - Vengeance, HyperX, Rip-Jaws). Top of the line PC's can be better off with Expensive memory modules which generally have lower latency rates.
If you are buying your PC for the First time, for studies, Internet and office work, and don't know how much to go for, go for any 2gb, 4gb or 8gb depending on your budget. You may increase it later as and when you need more. Normal Applications are find with 8gb. However, Games, CAD or other memory intensive applications or Servers Do need More. Generally Desktop motherboards now support till 16gb, 32gb or 64gb of Maximum Memory. Servers and Workstations go as high as 512Gb or even higher as well.
Check specifications of the motherboard you have selected to pick Memory Type accordingly. DDR3 aka DDR III