I only use tubeless for cross, the lack of choice and cost for road tubeless has put me off so far.
You put the sealant in either before you inflate the tyre, or once you've got a seal on the rim after inflating the tyre, but that depends on the tyre.
I've not bought some yet, but plan on getting a pair in the spring. They look good value for the price and ideal for the type of riding I do.