5. The gdb Debugger

gdb is the basic debugger for C and C++. Many Linux debuggers are based on it.
It is a command line debugger.
In order to use gdb one must use the -g flag when compiling!
Executing gdb is simple: gdb program_name.
gdb has an excellent built in help, you can type help from the gdb command line and get a list of stuff to get help on, or type help <something>, and get specific help on something - either a command or a topic name.
Other good sources for help on gdb are the gdb manual and the Little Unix Programming Group's Tutorial on gdb.