I am writingWe are writing
You are writing You are writing
He is writingThey are writing

This is called the present progressive tense.

It may be that you wish to be emphatic, and you say,

I do writeWe do write
You do writeYou do write
He does write They do write

This is called the emphatic present tense.

The past tense indicates that the action took place in past time; as,

I wroteWe wrote
You wrote You wrote
He wroteThey wrote

or, the past progressive; as,

I was writingWe were writing
You were writing You were writing
He was writingThey were writing