Tenses

Present simple = I write

→ statement, habit, now

Present continuous = I am writing

→ action, now

Present perfect = I have written

→ statement, habit, past, effect on present

Present perfect continuous = I have been writing

→ action, past still going on in present

Past simple = I wrote

→ statement, habit, past

Past continuous = I was writing

→ action, past

Past perfect = I had written

→ statement, habit, past, before other action

Past perfect continuous = i had been writing

→ action, past, before other action