No such thing as a dumb question - except for the one you don't ask. However, try using the search function - I think you'll find there's plenty of threads about this already.
But...
Check the oil like you do in your car. Change it every 100 hours or once a season.
I'm sorry - Don't understand the question. There is a dip stick just like in a car to check the oil. Your boat should have a remote drainto change the oil . Warm up the engine (hook up muffs to the water intake), remove the drain plug and the remote oil drain should be attached. Remove the nut and let the oil drain. Remove the filter and change. The oil may drain faster with the filter off.