Transporter is the van version, usually comes with seat only on the front row (driver/single or double passenger). On some double passenger seats, the backrest folds forwards.
Kombi has a second row, and has 5 or 6 seats. The second row either has a double seat plus a single seat, or a 3 seat bench. These are removable. If it has the 2/1 option, again the backrest folds forward onto the seat base on the double, but the single tilts forwards. Again, this is removable. These seats aren’t easy to take out single-handedly.
None of them fold flat to the floor, and sit about 18 inches above it
For a third row, you can get either the Shuttle or the Caravelle.
The Shuttle usually has the Kombi seats in rows 1 & 2, and the third row normally has a 3 seat bench. Again, the backrest folds onto the seat base, but it sits the same height above the floor as row 2, and is removable.
The Caravelle normally has 2 seats in row 1, 2 sliding (fore/aft) and turning seats in row 2, and a sliding 3 seat bench on row 3. Backrests fold onto seat bases as above for both, and they can be removed, but they’re really heavy, and you need to shuffle them along the sliding rails (having removed the “plugs” which allow the sliders to lift out). Getting them back in can be a ‘mare! The third row bench on some models will also fold flat backwards to make a “bed”, but it needs other parts behind it. Again, they’re about 18 inches above the floor.
This loosely cover the factory versions. As Jeff says above, you can retrofit any combination of seats to a basic Transporter van, but it needs drilling, seat belts fitting if you want to carry people, and a fair bit of cash!