Well I just read book in my friend house and there I notice that there was sentence like
He knows how to do that task
but what if I use it like
He know how to do that task
That thing is still confusing me and I don't the key difference because I am just in process of learning.
Best Answer
I don't think that I am adding anything new here, but this may clear up a couple of points.
In the present simple (affirmative), the form used for all persons except the third person singular of all verbs (except BE and the modals) is the same as first form/base form/bare infinitive:
In the third person singular of all verbs (except BE and the modals), an -s is added to the first form. There may be other slight changes, such as the addition of an e before the -s, but there is always an -s ending:
In the negative and interrogative form, we use the bare infinitive of the verb with the auxiliary DO. It is the auxiliary that adds the ending in the third person singular:
I/you/we/they do not know, do not play, do not try, do not do, do not wash
he/she/it/the boy/the girl/Peter does not know, does not play, does not try, does not do, does not wash
Do I/you/we/they know?, play?, try?, do?, wash?
Does he/she/it/the boy/the girl/Peter know?, play?, try?, do?, wash?