The Tags plugin allows one to quickly jump to definitions of class, methods, variables, etc... in source files. ctags is required for generating tag index files.
Tags was originally written by Kenrick Drew, but I am now maintaining it.
Here's a screen shot of Tags Tag Stack which displays where you've jumped to tags from and allows you to return to those locations.
This is a copy of the User's Guide which comes with the plugin.
Using jEdit's Plugin Manager is the easiest way to install, but you may also download it below.