Here are some hints for you graph.
We're graphing distance as a function of time. So the x axis should represent time, and the y axis should represent distance.
You know the "rate" at which distance is changing. This rate should be the _____ of your function for a certain time (do you know which word goes in the blank?).
Bonus hint in case you don't know the word:
d = 3t (this is a formula for a man who is walking at 3 miles per hour).