Problem with propeller on mercruiser?

i have a maxum 1800 sr 3.0 mercruiser engine. I took it out and when I put it into gear,the prop did not spin and the boat go nowhere. When i give it more gas the prop isn't moving any faster. after pulling it out i notice That the exhaust bellow had a hole, i would like some more info how the prop moves an help on ho tot fix my problem i also notice that the speed gauge ws at zero the whole time.any suggestion please help..... im new at boating