The seat has a tee that connects to the toilet supply line.
The supply line goes to the tee and the tee goes to the seat and the toilet tank.
You also need a 120v GFI outlet to plug the seat in to. The seat comes with a 3 foot cord so it it is usually less than 2 foot away.
Any one can install they are very easy. The electrical may be tricky.
Toto washlet seats will fit any toilet as long as it has a 90 deg angle. If you have a toilet that has a curved back us the E200.
You can go to their Washlet web site but be prepared for naked butts.