They also offer a reactor. Their gauges, regulators, solenoids and valves seem very overpriced. Also, be careful that stuff you buy is compatible with the CO2 bottles offered in your country. German fittings don't work with American bottles, for example. The CO2 regulator should be set to about 20 psi on the output.
Typical regulators get a little flaky at pressures below that.
There are all kinds of ways to get the CO2 into the water. The basic idea is to get the CO2 bubbles in the water and keep them in contact with the water as long as possible. The simplest is to bubble CO2 from a airstone on the bottom and have the CO2 bubbles come up below a powerhead or filter outlet so they get pushed around the aquarium. Get a good airstone so the bubbles are as fine as possible. The CO2 can also be directed into the intake of a canister filter, giving it plenty of time to mix before it comes out the outlet.