There are a lot of pool tutor and lesson websites around that offer many articles based on how you can learn to play pool and what the various tricks of the trade are when you have a pool cue in your hand.
Personally, I'm of the opinion that most of the pool tutor sites are not going to show you as much as you can learn yourself by spending time on a pool table (whether it's online or not). There's just nothing that compares to actual hours spent on a table, trying the shots yourself and coming across problems or difficult situations that you have to get yourself out of while you're playing a real oponent.
Lessons in the real world can't be beaten. If you have someone you know that is a good pool tutor and you can get them to take you for some lessons as you're playing them in a game, you'll do well. That can be pretty hard though as for most of us the people that are better than us are the one's we're playing against in competitions! There's a serious catch-22 going on there.
With online pool tutorials, you're only ever going to learn about the specifics of the game your playing in and as each pool game is different then you're going to have to go through a lot of different pool lessons if you play at more than one site. This is really a good reason for sticking to a single site and spending more of your time on it. You'll get better and better at the particular game you're playing and eventually you may be able to out-play others on the game.
So, the main thing to remember in looking for the right pool tutor and lessons is that the real-world cannot be beaten and that when you're online, stick to the site you're planning on playing on for quite a while as each site changes their own physics of the ball just a little to suit their own game.