How do you use mosaics once you have them in your wallet?
Hello!
AFAIK, A mosaic is an asset in the NEM Blockchain, because it can be created by everyone (paying a fee), it comes with different use cases.
So, usually, when you own a mosaic, the primary owner (who paid the fee to create it) publish the reason or the meaning of it.
Some user cases:
- ICO (Initial Coin Offering)
- A coin for a website or the representation of gems in a game
- Just for fun
Answering your question, what you can do with a mosaic is exchange it by some other asset, like XEM or a sword in a game. Again, the creator should publish the meaning and how to use the mosaic.
When the new release comes, Catapult, I think that will be more features around mosaics and namespaces. We will see 
Reference to official blog post
Best,
But how can you actually use them, I can’t seem to do anything thing with
them in my wallet they are just there?
You can send them to another people, just go to Send section and check Mosaic transfer.
I attach a picture of how it should be displayed 
Ah very good and can they be exchanged for xem somehow?
AFAIK, there’s not a easy way to do that nowadays. Must be someone that wants to exchange that asset by XEM somewhere, mainly the asset’s owner.