There are many vidoes on the net but basically, you are basically conditioning the dog to respond. First you make the dog associate the click with a treat - so repeatedly and ramdomly click and immediately treat.
Once the dog knows there will be a treat when ever it hears a click, you can start training. What the click does is allow an instant positive reward - the promise of a treat rather than the treat itself (which must always follow) - so it is a lot easier to train a behaviour. You don't have the delay of getting the treat out of your pocket, bag etc and don't distract the dog from the behaviour.
You can 'mould' a behaviour - leading into a sit, down, heel etc with a treat then click and reward when the behaviour occurs or you can 'free form' which is sitting around, clicker in hand, treat in pocket until the dog accidentally does what you want. I tend not to free form as the dogs then wonder what they did to get the click and get a bit over excited.
Once the dog is doing the behaviour to get the click/treat, introduce a hand command and/or voice command. Say it as dog does behaviour. Gradually, say it before dog does behaviour and click/treat when he is obeying on command.
Probably best to google for a video as I'm quite rubbish at explaining clicker training lol.