The Chimera User's Guide contains three main sections:
Chimera documentation, including the User's Guide, is bundled with each release. Your local copy of the documentation can be accessed and searched via the Chimera Help menu. Use of the bundled documentation is recommended because it is synchronized with the locally installed version of Chimera. Current development and latest production release versions of the User's Guide are available as links from the Chimera home page's documentation index.
A search tool is not provided for this locally-installed Chimera documentation, but you can search the Chimera documentation at the UCSF Computer Graphics Laboratory (CGL) web site. The documentation at the CGL site reflects a current development version of Chimera rather than the version you have installed. Although differences will be usually be minor, you may want to check the locally installed pages corresponding to the CGL pages retrieved in your search.