Question for all you gimp users

[Mike21]

I recently just downloaded gimp because I didn't want to pay for photoshop. So I guess I am the noob of all noobs with gimp. Anyways... I was trying to make a sig bar yesterday, and I wanted to change the foreground and background colors and when I clicked on another color it stayed the same. So my colors were black and white no matter what I tried. So is there anything I am doing wrong? Please explain to me.
Thanks in advnce