How do you tell that? Will the manual say it or is it apparent from looking at the machine?
There are two kinds of mowers out there:
(a) Flywheel brake (b) Blade Brake Clutch
Flywheel Brake type mowers are the most common. The blade is bolted directly the the engine; if the engine is running, the blade is spinning. They require you to pull back on the blade control lever and hold it in position to start and run the mower. When you let go of the lever, the engine's ignition is stopped and a brake is applied to the engine flywheel to make it stop spinning < 3 seconds. You have to pull back on the lever every time you want to restart the mower. With the lever released and the flywheel brake engaged, it should be hard / impossible to pull the starter rope and make the engine turn.
Blade Brake Clutch models feature a clutch device between the blade and engine. You can usually start the engine without holding any levers or controls in place. After the engine is started, you engage a blade control lever, usually a 2-step process. On Honda mowers, there's a yellow button that must be pressed in, then a lever moved into position. This engages the blade clutch and the blade starts to spin. Release the lever and the blade clutch stops the blades, but the engine continues to run.
On the back edge of the mower deck, you should see a model name and serial number; if you'll share the serial number with me, I can look up service details for you; it's in the form of "MXXX-1234567"