In English, we have just one past tense. In Spanish, there are two: the preterite and the imperfect. Here's how to tell when you can use each.
Online activities from the Realidades textbook
Book 2 Chapter 5A p. 248, 5B p. 277
Grammar video
Online activities from the Exprésate textbook
Book 2 Chapter 8A p. 290
Practice the Preterite vs. the Imperfect
Grammar explanations with self-correcting exercises
Preterite vs. Imperfect
Preterite vs Imperfect 2
Preterite vs Imperfect 3
Preterite vs Imperfect Review
Detailed grammar explanations with self-correcting exercises
The Imperfect and Preterite contrasted
Self-correcting exercises
Preterite vs Imperfect
Videos and interactive activities to learn Spanish online
Online Dictionary, Verb Conjugator, and Language Forums
Excellent grammar explanations with video
Imperfect vs. Preterite
Imperfect vs. Preterite Part 2
Online practice and games
Music videos and activities for practice
Pretérito v. imperfecto
Trigger phrases
Conjugation practice
Video interviews, podcasts, and grammar explanations
Online Grammar Lessons with worksheets