No need to get confused just yet. Paylines aren't the only line you stand in. In the world of gaming slots, the payline is a form of channels that connect the reels. Depending on the number of reels in a slot game, say for example a 5 reel slot game will have anywhere from 8-10 different symbols that can pop up from just one reel. This allows the paylines to cover a path with many variable routes across the 5 reels which may result in winning a combination over the reels. The higher the payline number, the better the chances to have a possible combo that can be won.
Some paylines are a low as 5 and go up to 25 or more. In some massive payline games there are even 1024 paylines are possible in the Multi-way win slots. How that's possible to have so many paylines is anyone's guess but then again, paylines do have an effect on the chances of better odds on a game. Since it's totally random you need all the help you can get. With paylines this can add to the rest of the goodies included in a slot game.
Each payline will cost a certain coin amount that is waged from the player. Some games allow as little as a penny to play and some can play for a dollar per payline. It depends on how much is waged that can get quite expensive after just a few spins in the game. The best odds help a player win things like extra spins or bonuses that allow for the game to last longer but the paylines still need to have some kind of waged amount in order to capture the combo should it come up in a random roll.