I second the recommendation of Starting Strength or StrongLifts. I would buy the Starting Strength book - it is surprisingly good to read about how to do the exercises. It has a huge amount of info. StrongLifts site is also terrific and has a huge amount of info.
I started when I was 35, after two decades of putzing around with little results. I'm thin, and went to the gym fairly regularly, but previously didn't have a program to actually add real muscle. After several months of Starting Strength, I was transformed. I'm still a thin guy, but with a decent build.
A few other notes:
Depending on your gym - you will stand out because you don't spend hours doing isolation exercises. Ignore others, after a while you will stand out only in a good way.
I didn't do power cleans. If you are serious about strength and power, then I think learning them is a good idea. I just wanted to look better and build muscle - I didn't need power cleans for that and the additional risk of injury.
I have had back problems before, during and after starting strength. I no longer do deadlifts or heavy barbell squats. I miss them, but so be it. If you have good form, and no structural problems with your back bones or muscle, then they are proven to be safe exercises if done correctly, and unmatched in building muscle. It was immensely satisfying when I hit new personal bests in squats - getting close to 1.5 times body weight in 3 sets of 5.