I have some friends who are retired, and travel multiple times a year taking advantage of timeshares they have purchased. A couple years ago while my wife and I were on a cruise, we met up with them is Cozumel where they had been staying for a couple weeks already.

What are timeshares? How do timeshares work?
When you buy a timeshare, you are buying a fractional part of a piece of property. You might be a 1/52 owner of the property, entitling you to use it for one week a year. So timeshares are usually used as vacation property. So for that reason, timeshares are usually located in popular vacation destinations. There will be plenty of other owners of the same piece of property who will also be using the property throughout the year. The timeshare will be managed, and it will need to be maintained, so there will be annual fees for maintenance, utilities, and taxes.
There are both deeded and non-deeded timeshares. Owners of deeded timeshares are actually partial owners. Owners of non-deeded timeshares are more like members of a club that gives you the right to use a property.
Shares of a timeshare might only be used at certain times of the year. So shares for popular times might be more expensive.
Besides buying, you may also sell timeshares. The sale of timeshares may also mean more fees in the way a transaction fee and a recording fee. There might potentially be other costs as well.
Don’t forget that if you own a timeshare in some other country, that in order to use it, you actually have to get there. So don’t forget about travel costs.
A timeshare doesn’t move. So you will have a place to go every year. The same place. If you like going to the same place every year, then great! But maybe you would like to go different places. Other people own timeshares too. So it is possible to trade the use of timeshares. Since the use of different timeshares may have different values, there are point systems. There are companies that will facilitate the swaps of trading of timeshares.
Another possibility is that you can rent your timeshare out.
Beware when buying timeshares. Some places may use hardsell tactics. Make sure you know exactly what you are getting, and how much you are paying. There are also scams involving timeshares.

Books on timeshares:
Timeshare Vacations For Dummies

Simplifying Timeshare: Vacation Ownership-the Complete How to

The Insider’s Guide to U.S. Timeshares (635 resorts)

Developing Timeshare and Vacation – Ownership Properties

Surviving a Timeshare Presentation

Blaggers: Adventures Inside the Sun-Kissed but Murky World of Holiday Timeshare