Konohamaru is an academy student of the Hidden Leaf Village at the beginning of the series, who wants to become the Hokage. After an unsuccessful attempt to fight his grandfather, the Third Hokage, Konohamaru starts to follow Naruto and makes him his teacher. He learns that even though Ebisu claims to be a shortcut, there is, in reality, no easy way to become Hokage, which Ebisu confirms himself later. Konohamaru then gives up on Naruto and declares him his rival.
The two of them often compete with the Sexy Technique, and naturally, Naruto always wins. Usually that is followed by Konohamaru saying something like: "Just you wait, next time I'll beat you!" Konohamaru also always looked up to Naruto and they have made a very deep and trustful relationship.
Naruto is also the one who taught Konohamaru the Rasengan. It is, of course, smaller and weaker than Naruto's, but its power is also great. We saw him use it for the first time against one of the Pein Paths, in the Konoha Invasion arc.