Welcome--you'll find a ton of useful information by searching through the forums. In terms of combos, MK is much different than Street Fighter in that combos are mostly done using canned strings (these can be found in the move list within game, or, of course, in character specific combo threads here on the forum). These strings in combination with special moves are the building blocks for combos opposed to SF using links and building combos from individual hits.
A very basic example of this would be:
Sub-Zero: Back Punch, Back Punch cancel into Iceball. Once frozen, Back Punch, Front Punch, Back Kick cancel into Slide.
Here Iceball and Slide are specials and can be cancelled from particular strings. Back Punch, Back Punch is a two hit canned combo. Also, the three hits after the opponent is frozen is a canned combo. Cancelling specials from hits is just buffering the command in while the animation is occurring during the canned combo.
Once you get into it, you will find certain characters and combos that use single hits to build combos, but the above is a general starting point for a new player trying to understand the system. I hope that it's helpful.
