Present Perfect
Finished past action: Il a cuisiné.
An action which lasted a certain amount of time: Elle a étudié au lycée pendant trois ans.
An action which has been repeated several times: Il a sonné quatre fois.
A series of actions: Il a pris la glace, il a payé le vendeur et il est parti.
Imperfect
Non finished past action: Elle cuisinait.
An action which is a habit: Il se promenait tous les jours.
A description set in the past: Le soleil brillait.
Expresses a state: Elle était petite.
Two simultaneous actions set in the past: Quand je courais, il sautait.