Typically, The "F-Keys" as they are known, are specific to the particular application you are using (firefox, Photoshop... etc.). As a general rule, the F1 key brings up some help documentation.
The primary mouse button would be the left-click.
Without it you wouldn't be able to open/run programs with your mouse. Also people use the left-click more than right.
You can make either button...
Interestingly enough, before it became the Furniture Capital of the US (which it no longer is), Grand Rapids, Michigan was the Button Capital of the US. In the old factories along the Grand River...