The alarm will sound continuously if you lose oil pressure or if your coolant temperature gets too high. If the drive fluid in the reservoir gets too low, it will sound intermittently.
The blower should run by turning it on with the dash switch, otherwise someone mis-wired it. Some people like to leave it run while idling or even while underway.
I love these types of shore power cords with the red LED. They let you know right away if the breaker on the pole is in the ON position.
There should also be a breaker near the boat's shore power plug. Make sure that is turned on.
The meter tells you how much voltage you have coming into the boat's panel. The polarity light warns you if the HOT and NEUTRAL are reversed. If they are reversed, things will function, but there is a good chance of equipment damage and/or personal harm.
Even though you've already purchased the boat, you may want to have it surveyed. A surveyor will find things you probably don't want to know about, but at least you'll know what needs to be dealt with promptly and what can wait until the off-season.
Be sure to hang out with fellow boaters and find a good trustworthy marine mechanic. You will never stop learning.