
Okay. :) First off, you click and treat until you notice that the dog understands the click. I did this with my 9 week old pup yesterday, and it only took about 5 clicks and treats before she realised that aha! that funny sound means a sausage piece appears! You WILL notice, because after the click the dog will look for the treat.
Secondly, you can start with anything and it probably would be easier to pick something he doesn't already know, but it needs to be easy!
Thirdly, it will vary from dog to dog when you withhold a click and wait for the dog to work something out so it's impossible to say. Some dogs will quickly give up and feel "Oh no, it doesn't work anymore to do what used to produce the click, I give up!", others will instantly try something else. You'll just have to try and see what works for your dog. If he gets put off and stops doing what he did previously, you will have to start from scratch again and encourage even small attempts. (But this time it will be quicker no doubt.)
Not quite sure when to introduce the verbal command, in the class I go to we've never done it yet! But at home I do it fairly soon, such as yesterday with the pup within about 10 minutes she'd understood what sit meant after I first introduced the clicker for the first time and then clicked her for sitting, then added the word sit -it really was that quick.