The habitual aspect is a form of expression connoting repetition or continuous existence of a state of affairs.
The form [would + infinitive] is employed to talk about a habit or frequent action in a former time.
(These are in addition to the non-idiomatic combination of to use in the passive voice with an infinitive of purpose, as in A spoon is used to eat ice cream from a bowl.)
In the first case—the past habitual verbal form—it is followed by the infinitive (that is, the full expression consists of the verb used plus the to-infinitive).
[Used to + infinitive] expresses the lexical verb’s habitual aspect in the past tense, and is in the indicative mood and active voice.
On the other hand, when forming questions or negative sentences, modern prescriptive grammar dictates that the simple past is better.
[5][6][7] The verbal use of used to should not be confused with second case—the adjectival form—of the same expression, meaning "familiar with, accustomed to", as in I am used to this, we must get used to the cold.