Brenda,
As far as your other questions, the benefits of
travel insurance may be in two forms: Either as a secondary to your current health/credit card protection programs (that is, the insurance will pay after the primary does) or you can get Travel insurance as the primary, which pays immediately. i would recommend the latter (primary version), since many of our American health insurance providers do not cover in foreign countries.
If you get travel insurance as the secondary insurer to your current health insurance, I would call your normal provider and ask what they will cover in the ports of call and otu to sea.
Another great part of travel insurance is coverage should something happen and you can't go. Canelation coverage is normally part of it and you will get a refund up to the trip amount (or amount of coverage you requested, whichever is lower) should you have a death in the family, terrorists strike a place on your trip, you are burglurized, have a weather event at home, and other possible conditions (each plans have different conditions on this). This could include all prepaid costs including hotel and rental car deposits.
Besides cancelation, many policies cover you if you missed a connection and need to fly to a port to catch the ship enroute, a lost luggae stipend to replace your cloths, and other potential costs.
Here is an example of what my insurance covers:
Benefits
Trip Cancellation Protection (if the trip is canceled by me or the cruise for designated reasons) .....................Up to the trip cost
Bankruptcy and Default Protection (if the airline I am flying, Delta, goes bankrupt or Disney does, I can get a refund for unused services)..............Up to $20,000 per person
Trip Interruption (I need to cut my trip short due to injury, weather or illness) .........................................150% of the trip cancellation limit
Travel Delay (hotel/food costs for missing the boat) $500 (after 6 hours)
Missed Connection (dad'gum airlines!

)....................................$300
Loss of Baggage / Personal Effects (has some restrictions such as medication, but will pay for new cloths!).............$1,000 (primary benefit)
Baggage Delay (to tide me over until luggage hits the next port) ..........................................$200 (after 24 hours)
Emergency Medical and Dental (dental with this plan is $750, others may vary. This is important to me)...................$10,000 (primary benefit)
Emergency Medical Transportation (need to helo'd off liek the guy on the QM2 last month? see Coast Guard site for details)..............$50,000
24-hr Accidental Death & Dismemberment....$10,000
24-hr Assistance Services...........................Included
Flight Insurance (if you get it, refunds the cost of your plane tickets).........................................Optional $100,000 or $250,000
Medical Benefit Updgrade (i took this just to be safe)...........................Optional $25,000 Medical/ $100,000 Evacuation
Different plans have different benefits. Travel Insured (above) have higher rates ($175 for Laurie and I), but they are a good company with lots of coverage.
Good Luck!!