If you're accustomed to something, you're used to it. Being accustomed has to do with habits and lifestyle.
Anything you're accustomed to is a regular thing for you. A rich person is probably accustomed to fancy clothes, expensive food, and beautiful houses. A football player is accustomed to getting tackled and tackling other people. Office workers get accustomed to filling out forms and fixing the copy machine. We can also say an accustomed thing is a usual, customary thing. When you think of the word accustomed, think "nothing new here."