Present Simple

Structure of present simple
I work in a bank.	I don't (do not) work in a bank.	Do you work in a bank?
He works in a bank.	He doesn't (does not) work in a bank.	Does he work in a bank?

Present simple - common mistakes
Common mistakes	Correct version	Why?
I working in London.	I work in London.	The gerund ing form is not used in the present simple.
He work in London.	He works in London.	The third person he, she, it adds the letter s.
He work in London?	Does he work in London?	Questions - third person: does + subject + infinitive. All other persons: do + subject + infinitive.
Work he in London?	Does he work in London?
He not work in London.	He doesn't work in London.	Negatives - third person: subject + doesn't + infinitive. All other persons: subject + don't + infinitive.