Usage of 'used to'

• We use used to when we describe a habit in the past.
• We often use used to to contrast a past habit with what we do now.
• The past simple is also possible, but used to is more common.

Examples:

• Statements: I used to play tennis when I was a teenager.
• Negatives: I didn't use to play basketball when I studied at school.
• Question: Did you use to play football when you were little?

In summary, 'used to' is used to talk about past habits. The negative form is 'didn't use to,' and the question form is 'Did you use to?'