Like Limit, Pot-Limit is always listed as two dollar figures, say $1/$2. You're typically allowed to buy in for a minimum of ten times the smaller dollar figure with no maximum.
In Pot-Limit, the amount you're allowed to bet is the same as it would be in Limit, but the amount you're allowed to raise is equal to the size of the pot. For example, say you're playing in a $1/$2 Pot-Limit game and you're under the gun. The blinds in front of you are $1 and $2. If you want to play in the hand, your minimum call is $2, just as if it had been a Limit game.
If you want to raise, the pot is calculated as though you already had called. You're allowed to raise anywhere between the amount of the bet to call and the size of the pot. In the $1/$2 game we've been talking about here, if you're under the gun, you could raise anything from $2 up to $5 (the pot being the two blinds [$1 + $2], plus the theoretical "call" you would have made of the big blind [$2]: $2 + $2 + $1 = $5). Additional raises are handled similarly.
As you can see, it gets pricey fast (and with all this calculation, it's no wonder people never play it).