The Present Simple
We use the present simple to tell about someting that is a fact or a habit.
The present simple is the base form of the verb:
I work in London.
But with the third person singular (she/he/it), we add an –s:
She works in London.
Let's look at these sentences
I play tennis = Positive sentence
I don't play tennis Negative sentence
Do I play tennis? Question sentence
As you can see, it is only the "hoofdwerkwoord" ,or as we say in English, the base form you use in a sentence.