We use the Present Continuous to talk about things that are happening now:

     –  Mark is riding a horse.

     We also use it to talk about temporary situations.

     –  I’m having a lot of fun.
     –  I’m studying in college.

     Present continuous sentences are formed with the following structure:

     –  Affirmative sentences: subject + verb be (am/is/are) + verb (-ing form).

         Example: She is eating ice cream.

     –  Negative sentences: subject + verb be (am/is/are) + not + verb (-ing form).

         Example: He is not listening to music.

     –  Questions: verb be (am/is/are) + subject + verb (-ing form).

         Example: Are you studying English?

Practice this lesson here: Reading 3, PRCONT001.