My favourite TeX tutorial, which will turn you from beginner to expert and make you fall in love with TeX (maybe), is the book A Beginner's Book of TeX by Seroul and Levy. It comes highly recommended by Hans Hagen in the ConTeXt manual. (It's not free—published by Springer—but you can find it in the usual places you find books: libraries, whatever.)

The TeXbook by Knuth. See if you can find it in a library.