Some of the things you should do while your parts are in the brown truck heading for your front door is:
1. Download all up to date drivers.
2. Download all the component manuals
3. Read all the component manuals
4. Repeat step 3
There's usually pictures
As you didn't name the motherboard in question, it's impossible to answer.... not only do manufacturer's do it differently, even the same manufacturer will vary from board to board. In one set of boards they might be 1st and 3rd from CPU (left to right) ... on next set 2nd and 4th.