In a club, you are in a room, comparable to a sitting room, with other women. The clients are also in the room. They get the opportunity to chat and have a drink with different women. Then, they usually choose a woman to go into a separate room with them.
Keep in mind that most clubs get a n extra profit from the drinks they sell, which might mean there is a risk of drinking too much.
Most clubs operate via an opting-in system: the club owner pays taxes on your income to the tax authorities (belastingdienst). You are not an official employee, but do receive an income statement detailing your earnings and deductions.
In a private club (privéhuis), the sex workers are introduced to the client individually. If there are no clients, the women are often waiting in a back room, where clients are not allowed.