I fairly new to Myst-just started playing it about a week or so ago. I have been reading on other posts getting information, hints, ect. and was wondering, how many different worlds are there in Myst or am I just misunderstanding the game? I haven't been able to get anywhere except for the beginning. I have gotten into the spaceship and things like that but not into a different world. Any info will be appreciated. Thanks!!!

There are four Ages, IIRC. Selenitic (you get there through the spaceship), Mechanical (through the big gear), Channelwood (through the tree) and Stoneship (through the ship).

If you are in the spaceship and have entered the correct code on the sliders of the control panel, a book will appear in the spaceship's viewer. Click on that book and away you go.