I recently got married and one of the gifts my buddies gave me was a grinder. It is brand new. There is one side for grinding and the other side for sharpening stuff. I am clueless (bumfuzzled) about how to sharpen my lawnmower blade on it. For example, what angle do I hold the blade at and such? Any help will be apppreciated. Thanks.

I just try to follow the original angle of the blades and sharpen in the areas that were already sharp.
There's no point in trying to make it razor sharp. You'll soon find out that a very sharp mower blade doesn't stay sharp for long, but keeping it semi-sharp and taking the nicks out of the blade does make a better cut.