I'm mailling you.
>> I'm mailing you the (insert the receive rof the action).
     I'm mailing you the postcards.

They 're shopping.
>> They're shopping for (insert receiver of the action).
      They're shopping for tomorrow's party.

I'm watching the movie.  Correct!

Explanation:
1. Don't forget to make your sentences complete. To make them complete be sure to have the receiver of the action in your sentences.

Comment:
Thank you so much for this wonderful homework Elsa! I am looking forward for more improvements in your written homework. I hope to see you again next week!
-Teacher Joanna