What is the difference between the present perfect and the imperfect?

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.