You have already used the Possessive Articles in the Preaching of Lesson 08 but here now an overview  and background  to enjoy.
The Possessive Articles are one group of six which you have already been quickly introduced to in the first two lessons. So far you have worked with the following groups:

• definite articles like der, das, die, den
• indefinite articles like ein, eine, einen

and now we'll add one more:

• possessive articles like mein, meine, meinen

You might already notice that those look almost exactly like the indefinite articles and that's indeed the case. The good news is that they also behave the same way when it comes to what ending they take. A few examples:

Ich liebe einen Mann. I love "a" man.
Ich liebe meinen Mann.  I love "my" man.

Ich sehe eine Frau.
Ich sehe meine Frau.

Ich fahre ein Auto.
Ich fahre mein Auto.

The only difference here is in meaning ("a" vs "my") because possessive articles are all about, well, possession, who owns what. That's a good start, don't you think? But unlike with "ein" there are six different possessive articles, exactly as many as there are personal pronouns. 

1. ich - mein Auto - my car
2. du - dein Auto - your car
3. er - sein Auto - his car
   es - sein Auto - its car
   sie - ihr Auto - her car

1. wir - unser Auto - our car
2. ihr - euer Auto - your car, girls
3. sie - ihr Auto - their car
   Sie - Ihr Auto - your car, Sir.

Interesting Tidbits

If you take it step by step, like we do in this course, you'll soon get them sorted out. I highlighted the "ihr" which you can see is present 3x and each time means something completely different: her, you girls, they. Don't worry about this as I'll have a full Masterclass about this topic coming up later in this course. I just wanted to make you aware of this specialty.

Also just notice that there are uns (us) and unser (our) which behave differenctly and also "euch" (you girls) and "euer" (your "cat", girls). You don't have to remember these things. I just mention this to prepare your brain for the time that you have to deal with such things. And that'll be a lot later on your German learning journey.