Service is a general word often heard when dealing with customers. If you have gone anywhere to get your car repaired or bought something at a department store, then someone provided you with service. The service itself can be judged based on how well the clerk or worker helped you. It could also depend upon whether the worker was kind to you.
Sometimes service is excellent and sometimes it is terrible. In some service jobs, the workers rely on tips, which is money that is extra that a patron gives to the worker for doing a good job. Waitresses get tips. However, the difference between service is tips is that the service is the way the work was provided, and the tips are the reward.