No-limit (most often abbreviated "NL") poker means just that: There's no limit to how much of your stack you can bet or raise. At any point, you're welcome to move all of your chips into the middle - usually called "going all-in", but also known as "pushing" or "shoving". While there is no upper limit to how much you can bet, there is (virtually always) a lower limit: You have to raise at least as much as the previous bet. If no one has yet bet, the minimum bet is the size of the big blind. If someone has bet, the minimum raise is at least as much as that bet - but you are of course still free to move all-in (in case your stack isn't enough to double the previous bet). Adhering to the online rules of betting in no-limit is automatic; the sites will stop you from betting too much or too little, so you really can't fail.
Pot-limit (referred to as "PL", as you may have guessed) games also have a fairly descriptive name; the maximum you are allowed to bet in a pot-limit game is as much as is in the pot - that is, however big the pot is after you've called. Some examples are in order:
The blinds are 10/20, and 3 players limped in and the small blind completes (5 players), the pot will be 100. The first player to act is allowed to bet between 20 and 100. Makes perfect sense, right? Well, once you're not first to act, it gets a bit trickier - try this:
If the blinds are 10 and 20, and there is a limper before the action gets to you, this makes the pot a total of 50 (10+20+20). For you to "bet the pot" at this point means that you raise it to 90 - as you technically call before you raise, as opposed to raising it to 70. Think of it as "20 and another 70", if it makes it easier - there was 50 in the pot when it got to you, you needed to add another 20 to call before raising, and the total pot is then 70 which is as much as you're then allowed to raise. I'm told this paragraph makes good sense if its read slowly and several times.
Concerning the minimum bet or raise, the same rules for pot-limit as for no-limit apply, and just as for no-limit, the online sites will automatically make sure your bets are no more or less than they are allowed to be, so no need to worry about that. In fact, many sites have a "bet the pot" button available for these games, which then also shows you just how much that bet is.
The options at a no-limit table. I can fold, call ($.10) or raise. In the image, I have moved the slider to 6.75.
As a sidenote, it's worth mentioning that unless the table is deep-stacked, meaning that the stacks of the players are big in comparison to the size of the blinds (which they're usually not online), the pots will usually be big enough by the river that it's possible to go all-in. Another sidenote is that NL and PL games are sometimes referred to as "big bet poker".
So are these big bet games for you? A matter of preference, for sure. I want to dispel a few myths, however, in case they were influencing your judgment. I will refer to them as no-limit, but all statements are true for pot-limit as well.
1. You shouldn't play no-limit because you think it's macho. You think it sounds silly that someone would think that? You're right, it is silly - but trust me, there are loads of people who think that limit poker is for "cowards".
2. No-limit poker games are not devoid of "suck-outs." I often hear complains about how they can never push anyone off a draw in limit, regardless of how much they bet or raise, and that no-limit would be so much better. The former is true, the latter is doubtful; you will still get loose calls from people, and they will just as often hit their draws as in limit.
3. No-limit is not a part of some natural cycle that poker players go through. This is also something I see a lot, the "play limit until you get a grip of the game, but then it's time to move on to NL" argument. I do recommend that anyone starting to play poker should play limit, so while I agree with the basis of the reasoning, I still disagree with its suggestion that limit is nothing but a stepping-stone to no-limit.
Now that we've cleared that up, what's the real deal about no-limit? Well, you can control the pot size, which means you can dictate the poker odds, both pot- and implied odds. You can manipulate people in a way not possible in limit, and you can make bluffs that will hurt to call. You can lose your entire stack on one hand, and you can double up on pure luck. It's a difficult game, and arguably more difficult than limit poker. However, because it's more difficult, the expert players will be able to force beginners to make more mistakes, which in essence makes the game easier to beat - perhaps a bit ironic. I like to see it as no-limit providing a lot more rope for the poor players to hang themselves with, compared to limit. It's also worth to point out that no-limit is the most common (or at least the most popular) type of game for tournaments - read on.