'be used to' is an expression. It is not a tense. The structure is: subject + main verb be + used to + object
Example : be used to something / be used to doing something

'used to do' is use when talking about the past. It is not a tense but it is like a tense. It has a special structure. We use the structure used to do for the past only.The structure is:
subject + main verb use + to-infinitive
Example : He used to work.