Prefolds are similar to the old flat nappies but they're thicker so you don't have to fold them so much. They work well but they're not as simple as the other options:
They have a pocket in them where the absorbent insert goes. Easier to use but usually not quite as absorbent as prefold.
Then there are other variations, e.g. Ones where the absorbent inner clips onto the outer ("snap-in"), or even simpler ones that are one outer and inner combined ("all-in-one").
These are prefolds, with outers: https://www.amazon.com/gp/product/B002LR8VC4
Prefolds are similar to the old flat nappies but they're thicker so you don't have to fold them so much. They work well but they're not as simple as the other options:
These are pocket: https://www.amazon.com/gp/product/B00SWIA5LQ
They have a pocket in them where the absorbent insert goes. Easier to use but usually not quite as absorbent as prefold.
Then there are other variations, e.g. Ones where the absorbent inner clips onto the outer ("snap-in"), or even simpler ones that are one outer and inner combined ("all-in-one").