GDB is a very mature application, literally decades in the making, and is extremely well documented. The most convenient way to access that documentation, and the way most likely to provide documentation on the version of GDB actually installed, is through info gdb; this provides access to the GDB info file included in the GDB installation. In addition, man gdb offers more concise GDB information.
Red Hat also provides extensive GDB documentation on the following link:
Not all documented characteristics will apply to all instances of GDB because it is still in active development, and as such the capabilities vary (to some extent) depending on the platform and target for which it is built.
