Simple Past VS Present Perfect

Use

Simple Past	Present Perfect Simple
certain time in the past Example: I phoned Mary 2 minutes ago.	just / already / not yet Example: I have just phoned Mary.

Certain event in the past or how often so far?

Simple Past	Present Perfect Simple
certain event in the past Example: He went to Canada last summer.	whether / how often till now Example: Have you ever been to Canada? / I have been to Canada twice.

Emphasis on action or result?

Simple Past	Present Perfect Simple
Emphasis on action Example: I bought a new bike. (just telling what I did in the past.)	Emphasis on result Example: I have bought a new bike. (With this sentence I actually want to express that I have a new bike now.)

Signal Words

Simple Past	Present Perfect Simple
yesterday ... ago in 1990 the other day last ...	just already up to now until now / till now ever (not) yet so far lately / recently