USE OF COULD

Could we use to talk about the past, the present or the future.

Could is a past form of can 

                               STRUCTURE 

subject + could + main verb

Also could does not change its form, so the third person singular form does not end in "s"

The negative form                           contraction       

              

could not                                      couldn't: 

Questions                                                           Possitive

 Could he help you?                                       He could  help you