Tenses

Placing an action in time.

The three families

Past, present and future each come in simple, continuous and perfect forms. I wrote, I was writing, I had written all sit in the past but say different things about completion.

The present perfect links past to now: I have written it means it exists now.
Keep one tense within a passage unless the time genuinely shifts.

Irregular verbs

English keeps a few hundred verbs that do not take -ed. Go, went, gone and see, saw, seen have to be learned rather than derived.