If you are accustomed to something, you know it so well or have experienced it so often that it seems natural, unsurprising, or easy to deal with.
I was accustomed to being the only child at a table full of adults.
我习惯了作为唯一的孩子坐在一桌成人中间。
When your eyes become accustomed to darkness or bright light, they adjust so that you start to be able to see things, after not being able to see properly at first.
My eyes were becoming accustomed to the gloom and I was able to make out a door at one side of the room.
我的双眼逐渐适应了这种昏暗,能够看到那个房间的一侧有一扇门。