How does it work and how do you install it?
In the carb, the throttle plate is below the fuel and the choke plate is above the fuel. The motor turns over and pulls air through the carb which in turn pulls in fuel. Dry fuel lines do not give any fuel, so it takes a long time to pull fuel through the lines and into the carb. The choke plate blocks off the air so the fuel lines receive increased suction from the motor and thus fuel is pulled through the lines faster. It's a solution to dry fuel lines, but not a very good one.
With a primer, a hand operated pump squirts fuel into the carb. The ski starts right up. It's that simple.
Primer is better. Choke sucks.
Edit: To install... Buy a kit...
For a single carb, you simply remove the choke plate and rod, add the supplied fitting to the place where the choke rod was. Cut the reserve line, put the supplied T fitting to reconnect the reserve line. Connect the supplied primer hose to the T-fitting, then connect it to the primer pump. Run the second hose from the pump to the carb.
For a dual Carb, there's an addition T-fitting that goes after the pump but before the carb, connect the second line to that second T-fitting. Then, after putting both fittings on both carbs, connect lines to both sides of the second T-fitting and connect one of each of those 2 lines to each of the 2 carb fittings.
Warning: If you try to remove the choke plates while the carbs are on the ski, be careful not to drop the screws down the carb. That would suck. The reeds should catch them as long as you do not try to turn over the motor with them in there.