It's better to understand 1 stage first.... Starting off, we need an agenda, the top capacitor is C1. The bottom capacitor is C2. The left diode is D1, and the right diode is D2. First D1 lets the current through, charging C1.
Then, D2 allows current while D1 blocks current. It discharges C1 and charges C2. After that D1 lets the current through, charging C1.
Then, D2 allows current while D1 blocks current. It discharges C1 and charges C2.
Every cycle C2 charges more and more!
