How do i apply concealer and prevent it from creasing under my eyes?

I've never used make-up before, other than mascara and eye shadow. I'm starting to get dark circles under my eyes and I'm really insecure about what I look like in public. I heard that if you do not apply concealer properly it can crease and go off during the day. Can somebody tell me how to apply it and prevent it from creasing or wearing off. Can you also tell me if sweating take it off and (if it does) how to prevent it? Thank you so much :)