Execution of productions within Soar (running the decision cycle) can be started by d, e, or run. Execution can be stopped by pressing Control and C together (on the Macintosh, in some versions you use C-c and in others you hold down the Apple key, the one with the paddle on it, and type a period).
The d command runs Soar one decision cycle at a time. If no integer is given, then Soar runs 1 decision cycle. If you type "d forever" Soar will run until it is explicetly halted (e.g. either by achieving the top-level goal or having the stop character typed to it or if you press halt or choose 'stop' on the GUI, or type control-c under Unix). If an integer is given (e.g., d 5) then Soar will only continue processing for the given number of decision cycles.
Similarly, the e command processes a set number of elaboration cycles. It takes the same arguments as d.
The run command is the most versatile since it takes two arguments, one giving the number of cycles to be run, and the other specifying what type of thing to run. For example, run -d 3 runs for three DCs.
More help from The Soar tutorial help page.