Great question... Really, how does it work? What does it really do? Is it safe?
So, lets cut to the chase... we've all done it, but consider for a moment, remember a time where you stumbled, nearly tripping and falling? Feeling that inner twitch, that inner Uh OH moment? Well the conscious part of the mind just isn't powerful enough to fire off the millions of neurons that have to work in tandem to get the other foot out there in time to catch ourselves, but the subconscious does, and it pushes (shoves really) the conscious out of the way, for that brief moment you literally are at the will of your own bodies desire not to face plant. It was and is in that instant where the subconscious shoves the conscious aside that you feel that UH OH feeling, as the body goes into a form of automatic reactionary response.
So you asked, how does it help, how does it work. Lets take a look back, you're five years old, and reach up to grab the handle of a hot pot on the stove. not knowing that hot is going to become a whole new experience for you, and that is the point here, an experience that as you grab it, your body is already trying to let go of it before you even know why, and then the pain hits... the Subconscious immediately marks this experience down as a HOLY $%#^ and records this as a very bad experience not to be repeated. For the rest of your life you will always turn the handle in or around over the stove instead of sticking out as you don't want to make that mistake again even as an adult later in life. The point here is that the experience is recorded and codified by the subconscious to base future experiences on or against.
So how did it get into the subconscious? that's the real question / answer, you see I can sit here and tell you its going to rain tomorrow, a hundred thousand times, and it might get through to your Subconscious, Or we can tie it to a painful or pleasurable feeling thus tying an emotional component to a message. Finally the third way is literally move the subconscious UP in awareness, i.e., move the conscious out of the way, and let the subconscious take the information in directly. Here's the important part, what ever goes INTO the subconscious is literally our reality. If I said don't touch that it's hot. you would instantly recognize that hot in this context is dangerous and painful. Here's the cool part, how do you KNOW that hot is bad? Whatever gets written to the subconscious is REAL for you. Think of it like this. Open up your operating system and overwrite something or add in something, close the file and run that program, you would find that the new information is as real as HOT is.
That's the key you see, you can add new data, or your can replace old data with more current data (belief) and use that as part of your day to day operation. What goes into and recorded in your subconscious is literally our beliefs, what we gauge everything against.
How does hypnosis work, we literally help guide the mind to step aside and let you have access to your subconscious directly writing new data or overwriting old data, and then rebooting with the new information to work with.
There are of course a boat load of books out there taking this subject on in far more detail than what's here, but I think you can see the concept. Here's an example. You're scared of purple clowns. somewhere in your past (child state) an event of some form caused your subconscious to mark down an event as bad, could have been a clown startled you with purple cotton candy or something. Now as an adult you might see how this could initiate a problem for someone, and that problem grows with the individual to where even as an adult you just don't like clowns at all, no matter what the context is. How does Hypnosis HELP? here's where the power of your mind shines, with hypnosis (hyper critical focused state) you can be guided back to that time that place that even you have forgotten had occurred consciously. back to the event, but this time as an adult mind, where you can see the event for what it really is or was, and you can over write the emotional context, you can cut the ties to the event, and in that instant you find your current adult self has re-interpreted the event without the need to fear it any longer.
There has to be an understanding you see, should you continue operating your day to day life based on an understanding of an event based on your 8 year old mind? or would you like to shed that fear by reexamining the event with your adult mind?