A little confusing for those not used to it, the way Megaways slot machines work is actually quite simple. Essentially, they are based on three main features:
No paylines
There are no paylines per se on Megaways Slots. You win when you get at least one matching symbol on at least the first three reels. From there, the position of the symbols on the reels does not matter, only their number affects your win.
Variable number of symbols per reel
The number of symbols on each reel of a Megaways slot machine changes with each spin. It can be between two and seven. This changes the number of ways to win (the famous "ways"), as it is easier to win with 7 symbols on the first reels than with only two. The total number of ways to win is calculated by multiplying the number of symbols on each reel. The total number of "ways to win" is usually displayed in the game window.
Cascading wins
Cascading wins are a feature that gives you a chance to win even more money with each win. When you win, the winning symbols disappear. Those above them then fall down and new symbols are generated to fill the space that appeared at the top. The spin can go on for a very long time as long as you continue to get winning combinations from the disappearing symbols and the appearing new ones.