I thought I would break it down for you, because not everyone understands how this works. (This is meant to be helpful)
Servers base pay is usually $2.13-$2.85 per hour. Usually leaning toward to lower end. Yes, it is a federal law to taker servers pay up to min wage ($7.25 per hour) however many restaurants will alter/claim your tips are more than what they are to avoid doing this. Not all, but many.
Servers typically work at least one hour before and 2 hours after service to do side work. Side work is filling ketchup, sugar, rolling silverware, vacuuming, making the tea, cleaning the bathrooms etc etc.
In many restaurants the servers make the salads and desserts also.
At the end of the night the server is required to "tip out" the bartender, expeditor, busboy, and hostess. They typically give each of these people 1-3% of their total sales-not their total tips. Most managers will go back and check to make sure servers are properly tipping out the other people.
So when you tip a server you are supposed to give 15-20% Although many people give 10-25%.
One thing to mention-when you shaft your server. It actually costs them money. Because they will have to tap into the tips they made from other tables to tip out the way they are required to.
You are paying for the service you are using. You are using the server to bring you your food, fill your drinks etc. You get to choose how much you pay them-but it is the service you are paying for.
I hope this was helpful. NOT meant to start a debate, not to be rude. Many people do not know these things.