Read the instructions on the container.You will dilute it with water.
How much is up to you.
But if you use it straight try not to spray it on anything but the engine itself.
I usually take one of those 2 gallon fertilizer/insecticide sprayers and add 1 - 1 1/2 cups of cleaner then top it off with water. Pump it up and spray the engine down , useing the wand to get into the tight places , even where you can't see.
Then after it sits on there for 10-15 minuites , hose it off.