Do you know the difference between DON’T (do not) and DOESN’T (does not)?
Both auxilary verbs are used to make negative sentences in the Present Simple Tense.
The third person singular (he, she, it) takes doesn’t but I, you, we and they take don’t.
We don’t use our moblies all the time.
She doesn’t use her mobile all the time.
Try this online exercise and see if you are good at this part of the Present Simple Tense.