subject+used to+infinitive: expresses something you used to do but now you don't my grandfather used to smoke when he was young. Now, he doesn't. object+(be) used to +infinitive a knife is used to cut food. a keyboard is used to type words. scissors are used to cut paper and cloth. subject+(be)+noun/v+ing : expresses something you are familiar with or accustomed to do i'm used to the darkness, i don't fear darkness i'm used to living alone. he is used to walking in the desert.

used to do sth :意思为过去常常做某事 sth be used to do sth :某物被用做什么 be used to doing sth :“ to” 是介词所以需要用动名词-ing形式，意思为习惯于做某事 希望对你有帮助哈

a keyboard is used to type words= a keyboard is used for typing words.