I'm going to be a jerk and say RTFM, because configuring BIOS (and memory speed) is in the motherboard's manual.
I think that's a little mean especially considering how poorly some of the manuals are written.
For the most part, if you buy parts that are compatible with each other, you should be able to get the computer up and running with little fiddling in the BIOS. Using your RAM comment as an example, I've pulled information from the Details tab of this Asus 1155 P8B75-V
motherboard:Memory Standard DDR3 2200(O.C.)/2133(O.C.)/2000(O.C.)/1866(O.C.)/1600/1333/1066
Here the OC (Over Clocked) means that if you purchase DDR3 at these speeds, then you may need to fiddle with the settings to get them to work optimally. On the other hand, if you buy DDR3 1600 then the board should recognize it easily and run it at its proper setting. I recommend posting the components you plan to buy here and let us look them over. If we see something glaring, we'll let you know.
If you want to learn more about BIOS, the October 2009
edition of MPC has an article that helps explain some of the terms. UEFI is the successor to BIOS but many of the settings will be similarly labeled.
As for building a computer, there are a great number of "How Tos" on the website:How to set up a new PC the right wayHow to Build a Kick-Ass Gaming RigHow to build an AMD Crossfire Powerhouse
Do your research, but just understand that every build will have it's own unique quirks and you'll have to adjust as you go along. If you do have any problems, remain calm and explain the situation on the Free Clinic forum.
Hope this helps and good luck!