I use the second one for forward delete, which is possible after I installed a keyboard remapping program called doublecommand. It's quite useful, since one of my issue with mac was that their laptops didn't have forward delete which I use quite often.
fn+Delete = forward delete
There is one know as enter/return.
The other one is next to thelog on the right side of the space bar.
I never use the second one. How do you guys use it?