Because the seat/base is a new concept, I'm going to show how the seat locks into the base.
Here you can see 2 long slots in the side of the base. This is where a metal bar (next picture) attaches the seat to the base.
Here is the little metal bar, sticking out of the seat in lock mode. There are 4 of these on the seat. On by the knees, and one by the hips, on each side of the seat. When unlocked, the metal bar retracts into the seat shell.
There is a knob on each side of the seat to lock/unlock the seat from the base. To unlock, both knobs must be pushed in and turned at the same time. TO lock, you only have to turn 1.
There is a set of red flags in the seat to let you know when the seat is unlocked from the base. Here are 2 pictures of them unlocked:
Here is a picture of the seat when the flags are in locked position:
It's very easy to lock and unlock. But not easy enough that it would be unlocked accidentally. Even though the seat is 25 pounds (plus 10 more for the base), it's really very easy to switch from rear facing to forward facing, and back again.