This guide is made for beginners. Im sorry if i forgot some tricstabs.
I apologize for mistakes in the text cuz i cant eng very well.

You'll get stairstab by jumping on ur opponent's head and stab him in his neck.
Ways of doing Stairstab
-Long Jump
-Backwards
-On his head
-Beside his head

Variations
-Reverse Stairstab
-Anti-Stairstab
-Under-Stairstab
-Blind-Stairstab

When someone is chasing u, walk away behind the corner, charge behind them and you have split of second to backstab him.

Variations
-Reverse Cornerstab

By walking to the direction (for example left) he will follow you to that direction, than you quickly change direction (to the right). He will still follow left side, so u have small angle to backstab him.

Variations
-Reverse Matador

Sort of like "Stairstab" but now ure jumping from higher position so they will not see you coming.

This stab is bit harder and very occasional.
Ur enemy has to stand (or jump) above you wich wont happen that often. Than you simply look up and stab him in his back.

Ways of doing Understab
-If he is following you downstairs, walk back for the stab.
-If they jump from an elevation, make a quick matador on the ground.