The adjective comfortable describes something that makes you feel relaxed, like a comfortable couch that makes you want to curl up on it and take a nap.
In addition to describing things that feel good, like shoes that don't hurt your feet, comfortable can mean "feeling free from stress or worry." If you are comfortable around people, you can be yourself. It can also mean "secure" — a family that, though not rich, lives a comfortable lifestyle, meaning they have considerable savings, or you feeling comfortable speaking Spanish in Chile, meaning you trust your ability to communicate.