used to do sth. 过去常常现在不了
eg: I used to eat so much meat, now I love fruit then it.
used to sth./used to doing sth. 习惯了（to是介词了，接名词或动名词）
eg: I used to getting up early every morning.
be used to do sth. 被用于（被动语态）
eg: Wechat is used to be the most common instant communication client software nowdays.