The adjective entitled means you have a legal right to something. If you are entitled to your mother's house when she passes away, that means it's written in her will that she gave it to you.
Entitled is often used in a more casual way, to mean "allowed." For example, volunteers at the park clean-up are entitled to the water and snacks at the pavilion. Sometimes, though, people feel they are entitled to special treatment because they think they are more worthy than others. This usage of entitled came from the mid 15th century, when it referred to giving someone the title of an estate or property.