Well, you know how there are three ways to say "you" in German? There are three corresponding ways to say "your" as well. The word "your" is grammatically called a possessive determiner, and in German possessive determiners are declined in the same way as ein/eine (their ending changes according to the following noun).
The three "you"s:
The three "your"s:
...with the -e ending, for example for plurals:
Note that using lowercase ihr as a possessive determiner only means either "her" or "their".