Hands only, or with tools?
I do a LOT of theory reading (but not much hands on, sadly), and the general gist is you can do a few things:
1) break the lock or the knob. you shouldn't be touching it directly. You're trying to break the door around it or damage where it meets the frame so it doesn't connect together properly. You're using the rest of the door a bit like a lever to try to snap or otherwise detach the area around the knobs/locks. This is a purely brute force approach, and is the basic setup for most types of breaching. You can do this with kicking, pry bars in between the door/frame near the knob, or a battering ram. I would consider lockpicking an extension of this class of entry. If you're in a hurry, using a small arm of some kind to shoot a semi circle around the knob/lock so as to "cut" it out of the door frame should make a well placed kick much, much, much easier. This is commonly done with shotguns, but in theory could be done with a handgun in an emergency. Just be aware of the risk of pass through.
2) fuck up the hinges. This is a bit more complex, and reserved generally for when you have some sort of stupidly heavy duty lock that just won't fucking go. You can do this quietly, depending on the hing placement (just pry the pins out if you're on the same side as them, easy but not too quick) less quietly (some kind of cutting tool, but that takes a fucklong time), loud (a sledge hammer and a specific type of spike tool that shoves in to try to separate the door from the hinge joints. Much less common.) Or really fucking loudly, which involves firing a shotgun 2-6 times to damage the area around the hinges (on the door side of things) so that you can kick the door in easily because all the wieght is being supported by either 1 hinge or just the knob. Ideally, you want to make sure you get the top and middle hinges first, because this would give a kick placed in the center of the door more leverage against the bottom joint than trying to go perpendicular to the middle joint or competing with the significantly higher top joint relative to the position of the kick.
3) just fuck it all up. You aren't even trying to target the specific "easy" parts anymore. You just want to remove the door from the goddamn wall. This is crazy shit like bulldozers, duct taping a ring of detcord into the middle of the door, placing detcord all the way around where the door meets the frame, placing charges directly against the lock, or cutting the whole frame out of the wall. Another less known option would be boring a hole into a partially hollow door (usually steel) and filing it with either a liquid explosive, or water and then a suspended block of C4 (the water propagates the shock wave in new and interesting ways :D ) The only real reasons to consider this are
1) You can sneak up to the door, and have time to stage, but once you start you gotta GO.
2) The door is highly reinforced (steel, a metric fuck ton of locks, whatever) and you don't have time to try to pick the locks nor will hand tools or other methods be effective.
3) You really just don't like the person on the other side of the door.
4)You just don't give a fuck today.
5)projecting overwhelming force in the initial seconds of entry is a significantly important operational component. (IE, you have 60 guys and need a really big hole really fast to flood a building)
That's really all I got, I'm not much of an expert but if you have something specific I could maybe answer…..