EXAMPLE
We had complete the work.
Whenever you see the
verb have in any of its
forms (have, has, having,
had), be sure that the verb
that follows it is in the past
participle form.
They have went to the market.
In the first example, complete should be the past
participle completed because it is after had. In the
second example, went should be the past participle gone
because it is after have.