When is imperfect tenses used?
Basically the imperfect tense is used for repeated or habitual actions in the past. It is often used when the English uses such terms as "used to" or "would."
We used to go to the beach. Ibamos a la playa.
They would go to Spain in November. Iban a España en noviembre.
If you will check out the reference section, you will be able to find out more in depth about this.
Go to this link
They explain it a lot better than I could.
You can get there be clicking "More" up there ^, then Reference, then Spanish Verbs, Indicative > Imperfect