The following tutorials can be used to get started with TeXmacs. Notice that they are somewhat outdated, so some of the menu entries and keyboard shortcuts may have changed in the meanwhile.
TeXmacs quick start guide, an introduction by Nicolas Ratier, which fits on one A4.
TeXmacs in 60 minutes, a hands on tutorial by Andreas Seidl.
A tutorial on the Maxima plug-in, by Andrey Grozin.
A TeXmacs graphics tutorial, by Henri Lesourd.
Using plug-ins to insert technical figures, by Nicolas Ratier.
Customizing TeXmacs, by Nicolas Ratier.