Deal With
= take action to do something, especially to solve a problem
Ex: You can’t just ignore your problems. You need to “deal with” them.
Deal With It
= solve a challenge, endure a situation
Ex: She doesn’t love you anymore. “Deal with it.”
What’s the deal? = 2 meanings
1) = What’s happening?
Ex: “What’s the deal?” Are going out tonight?
2) = what’s the matter with you?