These words are very common in informal conversations and writing. Being able to speak these contracted forms makes your speech more natural and can also make you sound more like a native speaker! There are many many more contractions (CAN'T, WOULDN'T, COULD'VE, THERE'S) but that is for some other time!
Try changing the two words in each sentence into one:
1. He is from Argentina. _____________________________________________________________
2. You are my hero. _________________________________________________________________
3. You are not a student. ___________________________________________________________
5. They are my children. ____________________________________________________________
6. She is not hungry. ________________________________________________________________
7. I am thirsty. ______________________________________________________________________
8. We are almost home. ____________________________________________________________
9. They are going to dinner. _________________________________________________________
Important thing to remember!
They are = They're ≠ Their
(They are is the same as they're but it does not have the same meaning as their)
You are = You're ≠ Your
(You are is the same as you're but it does not have the same meaning as your)