We use the present simple tense for things that we do regularly and for facts, habits, truths and permanent situations.

We use the present continuous for things that are happening at the time we are speaking, for temporary situations, and for activities that are in progress.

We use the present perfect for life experiences in the past, recent past actions that are important now, and past situations that are still happening now, often with how long, for and since; with just, already, yet for recent events.

http://www.bbc.co.uk/learningenglish/english/course/intermediate/unit-1/session-2/activity-3