If you want to find out how textures work in Second Life, visit the in-world Texture Tutorial on Livingtree.
Just walk over the bridge, and into the sky dome, and you'll find a number of stations, each with an example of texture use. Touch the object, and you'll be given a notecard that explains what that thing is.
You'll start with a Texture Overview, then find out how to work with images. Next, you'll learn how to work with the Texture Tab of the Build Dialog, how to handle Transparency in SL (including some pitfalls.) Then you'll find out About Faces, learn what UV Maps are, and what kind of maps are on the various prim types. From there, you can go on to Animated Textures (where you can get free scripts to do all the different kinds of animation possible in SL.) Station 8 will teach you all about textures on the Avatar, with notecards detailing the good point and problems with each of the various UV Maps (often referred to as "templates" and a UV Suit you can wear.
Finally, you can pick up a notecard that puts it all together, and invites you to visit the Texture Library next door.
The whole thing is free, and you can spend as much time as you like there, examining the examples, and listening to the flowing water and birdsong, as you absorb the peaceful ambience of Livingtree Island.
There are also classes held in the Lecture Area behind the Tutorial from time to time. Watch the Events (or my Blog or Twitter) for times and subjects.