There are many different kinds of slot machines in Las Vegas. Some of the most popular are the video poker machines. These are the standard 5 card draw machines, all the way up to 100 play machines, where you can play 100 hands at a time.
Becoming more popular now are the 9 line slots. Usually these are themed slots (Adam's Family, I Dream of Jeanie, etc.) with a bonus round. These can actually be quite fun to play. Most are 1 - 5 credits a line, with a few exceptions.
Of course, there are the standard 3 - 5 reel slot machines, of various types. These are the typical "one-armed bandits". You can find them from $.05 all the way up to $100.00 a pull!
Finally, there are progressive machines. These aren't a specific "type" of slot machine, they can be any of the above, but there's a progressive jackpot involved. If you hit a royal flush on a video poker machine, or a specific combination of characters on a regular or 9 line slot machine, you will win the progressive jackpot. Progressive means that for every amount of money played, the big jackpot goes up by a specific amount. Some progressive machines can pay $1,000,000 or more! Megabucks, a 5 reel dollar slot machine, can pay many millions of dollars.