A common method of Marine Micro is the "stutter step". How is this Marine Stutter step done and when should it be used? For example is the Stutter step effective against Banelings, etc.
There are 4 methods to stutter step, but the concept is always the same.
Marine shoots, the "animation" is canceled by a move command, move command is stopped by some action and marine shoots again. Because the action to stop moving varies there are basically 4 different ways to stutter step and each has advantages and disadvantages.
shoot, move, Stop, shoot ...
This is the easiest to execute, as it involves only pressing 1 button. The problem with this is that while it works for the "front" Marines, the Marines in the back also stop moving, thus preventing them from forming a proper concave as they are too far away to shoot anyway. But in this version Marines can wander "a bit" off to some unwanted location, especially the Marines in the back might walk away from your destination, because of some enemy units.
shoot, move, Hold Position, shoot ...
This is also very easy to execute. It has similar problems as Stop, but you retain your formation. This is good for stutter stepping in a "Magic Box" to prevent splash damage. I would argue Hold Position is better than Stop.
shoot, move, Attack Move, shoot ...
This is the way to go. It is harder to execute as you have to press A and right click. But your Marines in the back still walk towards the front thus building a better concave. They still might wander off, but in most cases this is still better than Hold Position and Stop. Another bonus is that you can focus fire an enemy unit while stutter stepping.
shoot, move, Patrol, shoot ...
Very simmilar to Attack Move but you cannot focus fire an enemy unit.
As already pointed out in an other question the different methods different APM counts. Basically Hold and Stop require 170 to 240 and Attack Move and Patrol require 255 to 360 APM.
You should always stutter step if you can afford the APM and you get a benefit from moving towards or away from your opponent.
Marine stutter step is done by right clicking away from the enemy forces and then hitting A (for attack), then left clicking away from the army. This will cause the army to move away and then attack any enemy within range. You can also right click away, and hit S for the units to stop and they will then turn and fire as well. Or hitting H to hold. Or even using the patrol option. Using the stop or hold command requires one less action so I would think that would be more effective for APM usage. (I personally use the right click away, S, right click, S method).
Here is a video showing the A method:
But all the commands are essentially the same, you need to click away, and then have your units stop to fire, then click away again.
As far as when to use it, use it whenever you can to minimize damage taken to the marines/marauders, or when you're attacking and trying to close a gap so they can't run away.
Stutter step (without stim) is effective when running away from zerglings (without speed) in early game TvZ. It's also useful after you get stim and they have speed. Stutter step is only useful against banelings if you have stim and they are off creep without speed. If they have speed, you are better off splitting your marines (which takes a lot of practice).
It is also effective against protoss if you have stim and are attacking them. After you stutter step away enough to kill all the zealots, you can stutter step in to finish off their sentries and stalkers (Assuming you don't get forcefielded and killed). The same method can also be applied to attacking into a fortified position against terran using seige tanks and/or bunkers.
There are about a billion answers to this question, all depending on the situation.
The general mechanic of it is simply right-click in some direction - usually away from the opponent but sometimes offensively in the direction of the opponent - and then press stop. Then repeat those two easy steps in the rythm of the units attack speed, which is the hard part. Getting the right rythm down requires a lot of practice and for Marines and Marauders, you need to have different rythms for Stim and no-Stim.
The same technique also works for Tanks, Hellions, Stalkers and basically all other units, even Zealots can be used in the same way against Zerglings.
There are some custom maps that let you train your stutter step, though i don't have the name of any memorized. I think Dargleins micro trainer or such was one of them.
As for stutter stepping against banelings: