set some keys for the global control.

1) create a locator

2) go into your side view

3) set a key frame and position the locator on the end of the planted foot.

4) Then using the locator as a guide, go to frame 2, and slightly move the global control forward until the foot lines up with the locator.

5) go to frame 3 and do the same, do the same for 4,5,6 etc. until you come to the end of your walk cycle.

6) Then go into your graph editor and go to Curves > Post Infinity > cycle with offset (i think)

7) press play and...voila!

However, doing it this way (hence the word infinity) keeps the character walking forever. There is a way you can stop it when you choose, but i dont know how