The easiest way to understand the Paroli system is to look at an example – let’s say you bet one chip on black. If black shows up, you will just leave your original bet and your win, so a total of two chips, on the layout – this is the first progression.
If now you win again, you will leave your total of four chips on the betting area for the next round. One more win and you have made 8 chips already. If you want to go for one more progression (this would be number four) and you win, you would have made already 16 out of your original one chip. Theoretically you can do this for however long you want, depending on what you’ve personally decided in advance.
If you lose in-between, which is obviously going to happen quite frequently, especially if you are going for a higher number of progressions, it is not that big of a deal. Most of the chips you lost were the bank’s anyway, since your own original bet for each round was only one chip.