Since Donald Knuth gave the scientific community TeX and Leslie Lamport designed LaTeX on top, publishing and typesetting mathematics was revolutionized. Many packages and variations like AMS-LaTeX were designed on top of these. Nowadays many math journals provide LaTeX style files for typesetting your manuscript. The advantage is that the underlying TeX language is very stable, and the properly edited source file is readable and is very structured. This is very much unlike point-and-click WYSIWYG type of word processing systems. Numerous are the books available, documenting the extra packages and explaining the use of LaTeX, both on paper and on the Web (see e.g. the online wikibook). On different discussion forums, one may find many different opinions on which is the best book to learn LaTeX from. Which one best suites you will probably depend on your background and previous experience with typing and rendering manuscripts, but also on how urgent and/or how frequent you will need to use LaTeX, and/or what kind of exotic typesetting you need. In my opinion, for conventional mathematical papers, there is nothing surpassing LaTeX in one form or another. The problem with many of these books is often that they want to be as complete as possible and they describe all the features of the whole LaTeX language. This gives the impression of a quite steep learning curve, which it need not be. Grätzer, the author of this book, is also the author of one of these more "extensive" documents More Math into LaTeX (Springer, 2007). With its 620 pages, it is too much to get started.
Like so many other authors, Grätzer also wants to provide a shorter start-up introduction. Disregarding the appendices and the (extensive) index, the proper material of the extensive version has been reduced from 488 to 160 pages in this starters version. It is basically a revision of his earlier First Steps in LaTeX book (Birkhäuser, 1999). The book starts with a quick survey, and then explores a bit deeper how to typeset the text, the use of environments, (mathematical) formulas and arrays, and finally the global structure of the document (top matter, body, back matter). That should have you going a long way. Only then the reader is informed about defining his or her own commands and environments. For presentations, there is a short introduction to a "baby-version" of beamer, and a minimal description of TikZ to generate plots (or e.g. commuting diagrams). Grätzer has chosen for an AMS-like description and takes the amsart class as the basic one for typesetting the manuscript. Essential are the tables with text and math symbol commands that are listed as appendices. Certainly as a beginner, you will have to lookup these tables a lot. Somewhat surprising is the third appendix in which it is explained how you may get LaTeX running on your iPad. I am not as convinced as Grätzer seems to be that typesetting LaTeX documents on your iPad is a viable alternative. In exceptional emergency situations it might be an option, but still I doubt it.
Of course, reducing the full version to less than half, requires some shortcuts. For example downloading and installing the MikTex system (a LaTeX distribution) is almost disregarded, and the help of a colleague or friend is advised if it is too difficult for you. There are of course many alternatives to generate plots, the BibTeX description for bibliographies is very short, and for MakeIndex to generate an index one is referred to the extensive book. What is however quite interesting is that he manages to include his experience as a user into this booklet by inserting many "practical tips". These are guidelines to learn good practice from the start or to prevent errors that beginners will easily make, how to locate an error, or what may have caused a particular error, etc. Of course many sample tex files are available via the website of the book.
This may be seen as an alternative for several other introductions to LaTeX. For example the The Not So Short Introduction to LaTeX2ε by Tobias Oetiker that is available on the documentation site of the LaTeX project. That is more focused on the plain LaTeX2ε, while here focus is more on the AMS-LaTeX. Also the journals in which you want to publish that have their own style files will often provide a general introduction to use their package, although there is a basic package like AMS-(La)TeX underneath. Thus when it comes to the proper content of your paper, you will need more, and then, if you are a novice, this can be provided by a booklet like this one. Although, I have been using LaTeX for many years to produce many papers and even books, and I consider myself relatively experienced, there is always something to learn, even from an introduction like this one. After some time one is frozen in those ingrained habits of doing things, and it needs another vision to find out about alternative or better ways to do it. Hence this book might be interesting to read, not only for the beginner, but also for the experienced LaTeX user.