We provide a self-contained introduction to finite extensive games with perfect information. In these games players proceed in turns having, at each stage, finitely many moves to their disposal, each play always ends, and in each play the players have complete knowledge of the previously made moves. Almost all discussed results are well-known, but often they are not presented in an optimal form. Also, they usually appear in the literature aimed at economists or mathematicians, so the algorithmic or logical aspects are underrepresented.