What's the difference between Schon gut and alles klar?
I am using duolingo to learn german but it does not tell me the difference and the comments on the lesson aren't helping either. Duolingo just says they both mean all right, is one formal and the other informal?

Question

Answer

There are as well other meanings depending on the context:
1. When you want to calm down an overexcited person, you could use 'Schon gut!'.
2. When you want to stop someone talking/explaining something to you which does not interest you, you could use 'Schon gut!'. This could be taken as unfriendly by the other person.

'Alles klar?" as a question is often used instead of 'How are you?'.

Answer

It depends on the context. 
"Alles klar" is an idiomatic expression for "Is everything ok?" or "Everything is ok.".
Another possible meaning of "Alles klar?" "Do you understand everything?"

1.) You can use "Schon gut" in response to someone saying to you "Thank you". It's interchangeable for: 
Bitte.
Bitte schön.
Bitte sehr.
Es war mir ein Vergnügen!
Nichts zu danken.
Gern geschehen!
Gerne!
Example: Danke für deine Hilfe. (Thank you for your help.) - Schon gut.

2.) You can use "Schon gut" to express that something didn't caused you any problems or it wasn't that bad. In this case it's interchangeable for:
Keine Ursache.
(Das) geht (schon) in Ordnung.
Ist okay.
Example: Es tut mir leid, dass ich dein Kleid beschädigt habe. (I'm sorry that I damaged your dress.) - Schon gut.