http://www.collinsdictionary.com/dictionary/english/problem?showCookiePolicy=true http://www.collinsdictionary.com/dictionary/english-thesaurus/deal Definitions above. They are not close synonyms so if you have difficulty in distinguishing their meanings in a specific context, then I recommend you give us more information.

As in the difference between "What's your problem?" and "What's your deal?"? Both are casual speech used as a strong reaction to when someone is bothering you, and both are fairly common to hear. They are almost entirely the same in their meaning and usage. The one difference might be that "problem" in this context refers to something that is causing a person to be annoying just then, whereas "deal" would have the connotation that you are dealing with someone who is annoying all the time, or who is trying to do something shady. Like I said, it is casual speech, so it doesn't pay to over think about the differences. They are used interchangeably.

thank u Matt, I got it.

"It's not a big deal" means "it's not particularly important". In context, that may sometimes be very similar to "it's not a problem", but often could be very different. For instance:- "My car caught fire today, but it wasn't a big problem." "My car caught fire today, but it wasn't a big deal." (Both are similar.) "My friend got a promotion today, but she doesn't think it's a big deal." (Only "deal" would be appropriate here, because a promotion is a positive thing.) "Can you afford the cost of your son's medical treatment?" "It's not a big problem." (Saying "it's not a big deal" would be inappropriate here because obviously the medical treatment is important.)