If something is slangy, it has a lot of slang in it or it sounds like slang.
Slangy can make people think of informality, being cool, or talking with friends.
Examples:
Her speech is very slangy.
The book is written in a slangy way.
He has a slangy way of talking.
I don't understand your slangy words!
The movie is so slangy, it's like they're speaking a different language!
The slangy song is my favorite because it's so fun to sing along to.