• I  am used to animals.
  • I  used to smoke.

These two expressions look the same, but in fact they are completely different.

be used to

I  am used to getting up early.

be used to something
be used to doing something

be used to is an expression. It is not a tense. If I say "I am used to loud noise", it is like saying "I am accustomed to loud noise. It doesn't bother me."

Do not confuse be used to with the special structure used to do. They have different meanings.

Structure of be used to

The structure of be used to is:

subject+main verb
be		+used to+object

used to do

He  used to work.

We say used to do when talking about the past. It is not a tense but it is like a tense. It is a special structure. We use the structure used to do for the past only.

If I say "I used to smoke" it is like saying "I smoked in the past but I don't smoke now."

Do not confuse used to do with the expression be used to. They have different meanings.

Structure of used to do

The structure of used to do is:

subject+main verb
use		+to-infinitive

sources : Original Link