From here, there are various possibilities you can do: You can execute the current line (F10, gdb's "next" command), step into the functions (F11, gdb's "step" command), or run to the end of the function (F12, gdb's "finish" command). At every stage, KDevelop updates the variables shown at the left to their current values. You can also hover the mouse over a symbol in your code, e.g. a variable; KDevelop will then show the current value of that symbol and offer to stop the program during execution the next time this variable's value changes. If you know gdb, you can also click on the GDB tool button at the bottom and have the possibility to enter gdb commands, for example in order to change the value of a variable (for which there doesn't currently seem to be another way).
