A drawing takes place each week on Friday at 20:00 UTC. A winning number is calculated based on all bitcoin addresses that are participating in the current drawing and the time when the drawing is performed. The ticket that has the closest number to the winning number is the winning ticket. The prize pool is also split between the next three (or more) closest tickets (more details).
The bitcoin addresses that are used in the formula are the addresses from which payment was received when tickets were purchased.
After a drawing is finished, the prizes for the winning categories are calculated, and bitcoins are sent to the winning addresses. There are also statistics available for each drawing where the following information is provided: how many players have won a prize, what are the winning addresses for each prize category and the transaction ids to verify the transaction with any online block explorer.