We use the present simple for things that we do regularly and for permanent situations.

We use the present continuous for things that are happening now and for temporary situations.

We use the past simple tense when an action or situation happens and finishes in the past.

We use the present perfect to talk about our experiences in the past often with ever or never; to talk about situations that started in the past and are continuing now often with how long, for or since; to say whether an action has happened or not at the present time with just, already or yet.

We use the present continuous to talk about the future when we have made an arrangement to do something.

We use be going to + infinitive for future plans.

http://www.bbc.co.uk/learningenglish/english/course/lower-intermediate/unit-20/session-2/activity-3