The vast majority of the time the player makes a bet for the dealer. This is done by putting the tip on the edge of the betting circle, close to the dealer. Think of the tip as orbiting around your bet, where the betting circle is the path of the orbit. If you double down you may or may not also double the dealer’s tip. If you split then I believe you must also make another bet for the dealer. Sometimes when a player leaves the table he will just leave a tip for the dealer, like on a table in a restaurant.