I'm going to give a long answer to this question because it might be helpful to others:
1) Where to play?
There are all manners of casinos in Vegas. Those on the strip are by far the most expensive, in terms of table minimums. A tiny percentage of tables might be $3 minimum (I think Hooters advertises $3 blackjack) but mostly you're looking at $5. Your options are Downtown, or off-strip. I find Ellis Island kind of small and dark, and the last time I was there, there was pretty much nobody at the only crap table. But there are lots of off-strip places, Ellis Island, Tuscany, Hooters, if you go the opposite direction Palace Station, but my fairly strong recommendation would be Orleans. It's quite large and well-lighted, high ceilings give it a spacious feeling, and you can almost always find a $5 crap table and it's rare to not find a $5 blackjack table (but on weekend evenings, no promises). As noted elsewhere, they all have free drinks but you should tip the waitress a buck or two. The minimum Uber fare in Vegas is, I think, $7.75, and Orleans would be a minimum fare ride from Bellagio, or you could walk it if you're staying south or west of Bellagio. (You'll have to take Tropicana across the freeway.)
2) What to play?
If you don't want to learn the rules, you're pretty much stuck with slot machines on the money wheel (that spinner that has symbols or dollar bills on it). Slots have lousy odds, and in practice you can't really hope to win, only to lose slowly enough that your money lasts a while.
By far the best bet for the uninitiated is the pass line at craps. Find a site that explains it. I once calculated that I could play craps for an expected cost of $2.65 an hour, not including tips to the waitress. Don't play anything but the pass line and the free odds bets. The house advantage is 1.4% on the pass line and 0% (yes, no house advantage) on the free odds, but the other bets on the layout have house advantages up to 16.7%.
If you want to play anything else, read up on it. A terrific site is WizardsOfOdds.com, which has strategy and odds on about any game you'll find. But if you want to play blackjack but not learn the basis book strategy, you'll increase the house advantage a lot. (Also, don't play the side bets like Lucky Ladies or whatever else they have, because the house advantage on those bets runs up to 25%). There is blackjack and blackjack variations (my personal favorite is Blackjack Switch), 3-card poker, pai gow poker, and some other card games. But you have to learn the rules and the basic strategy.
Roulette looks pretty simple and it is, but the odds are awful. House advantage of 5.26%, 3 1/2 times as much as the pass line at craps.
Bacarat is very very simple, and you can put on a tux and pretend you're James Bond, but I haven't seen a bacarat table outside the high rollers lounge in forever. They have something called "Mini-bacarat" but I'm not familiar with it It's similar to blackjack but the rules for hitting are fixed for both the player and the dealer, and you can bet on either the player or the dealer (but the odds slightly favor the dealer so you pay a commission on winning bets on the dealer).
3) What to expect?
Expect to lose. Someone noted that $100 isn't much of a bankroll for a $5 minimum, and I agree. I would estimate that maybe 1 time in 10-15, I lose $100 in an hour. My long-run estimate may be $2.65 an hour, but as the famous economist John Maynard Keynes said, "In the long run, we are all dead." Hope to not lose much, or to have your money last a while. Have a good time. Drink until you can't tell the difference between "Blessed be Mordachai" and "Cursed be Hamaan." (Jewish joke.) Talk to people. If it's not fun, find something else to do. If you go downtown and it's dark, catch the light show on Fremont Street, or if you're on the strip, the fountain show at Bellagio (which I never get tired of).