Infinitive
I want to work
He has to sing.
This exercise is easy to do.
Let him have one.

Simple Present
POSITIVE : I play tennis on Mondays.

NEGATIVE :They don't (do not) work in New York.

I like computers.
I don't like computers at all.
My friend likes computers.
My mum doesn't like computers at all.

QUESTION (Use the auxiliary do/does) : Does she know him?

Do you play football?
Does he play football?

Read more: http://www.englishclub.com/grammar/verbs-verb-forms_main.htm
http://www.englisch-hilfen.de/en/grammar/sim_pres.htm
http://www.englishpage.com/verbpage/simplepresent.html