LaTeX uses Donald Knuth's Computer Modern fonts by default[Using PostScript fonts with TeX]. This supplies three font families: serif, sans-serif and a typewriter (or monospaced) font (as well as the maths fonts which are discussed in §9.4.1. Maths Fonts). With each font family, you can change the shape and weight, as well as the size.
This book is also available as A4 PDF or 12.8cm x 9.6cm PDF or paperback (ISBN 978-1-909440-00-5).