If you intend to keep that engine for some time, purchase a factory "Bombardier" service manual that is specifically for that engine... ordered via it's model number that you'll find on a small plate on the port (left) transom bracket.
What is that Model number?
It's important to find the single specific Service Manual... NOT... one of those manuals that cover a half dozen engine or more as they will do nothing but confuse you.
If the engine has been sitting for some time, the carburetor is no doubt fouled, gummed, clogged, and will require cleaning and rebuilding..... rebuild/repair kits are available for something like $20 or so.
Basic trouble shooting would be: (spark plugs removed)
*Check compression - What is the compression psi of the individual cylinders?
*Check spark - The spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!
You need to explain more clearly.... Example: When engaged in gear, no gas, just idle <-- that doesn't spell the problem out.... As far as anything missing, we wouldn't know unless you explain in detail what you're speaking of.
The fact that you know nothing about outboards doesn't make you a dummy... it's just something new to you, and we'll help whenever we can. Let us know what you find.