... Considering one possible example, to a group one can associate its ends the ?points at infinity? of its graph. For instance, $\mathbb Z$ has two ends (plus and minus infinity), $\mathbb Z^2$ has one (infinity), free group with two generators has infinitely many. ... We will explain this theory, and, if the time permits, will say a few words on what is left to prove the Stallings theorem, how a group with infinitely many ends can be forced to act on a tree. ...