BnB stands for bread and butter, which is an expression often used here to refer to damaging combos. Learning how to play fighting games to a good level takes time. I'm still working at it (and I have definitely improved a lot since the beginning).
I agree with oblivioner: it is better if you start with the basics of the game. Learn the system well. The BnBs can wait. Again: here's the link to Tom Brady's guide:
http://testyourmight.com/threads/mkx-system-guide.49846/
While reading that and the posts that you find around here, you'll probably need this:
http://en.wiktionary.org/wiki/Appendix:Glossary_of_fighting_games
I recommend you not to discover your own combos for now, because you will most likely find stuff already found by someone else. Once you have grasped the system, go to practice and find a character which apparently suits you. Come here again and look at that character's forum. You should find a thread with BnBs. Start practicing what more experienced users found and posted there. It will take hours before those BnBs come out most of the time. Once they come out really naturally and don't take effort, start playing the AI on maximum difficulty.
I am still learning footsies, and I recommend you to learn that concept as well, and try to apply it to MKX as best as you can. The most helpful tutorial on footsies that I have found so far is this one:
I know it says "Injustice". The concept of footsies is common to every fighting game, so even if MKX has a different system and different footsies, you can learn the concept from that video.
Another important thing to improve your game is reading and understanding frame data. I know of very good players who don't know a thing about frames, so I would say that you leave this to the end. It has helped a lot my game. I think it helps you build confidence so that you don't get frightened and block all the time when you could be punishing or even pressuring your opponent. I've found two very good guides for understanding frame data on this site:
1)
http://testyourmight.com/threads/general-mk9-frame-data-info.15988/
2)
http://testyourmight.com/threads/how-to-read-understand-and-calculate-frame-data-in-mkx.49708/
The first one says "MK9". You should just read the first part (until "useful formulas"), and then go on to the second one, which is MKX specific. Or you can go directly to the second one. I think reading both will help you the most, since frame data is one of the most difficult concepts to grasp.
I have been playing "seriously" for three or four years now, and I still do all this stuff that I told you to do. Also, if you have any doubts, you can go to my profile and post some questions there. I will provide the best answer I can.