Past participles
The Past Participle is like the "-ed" form in English. It's used as an adjective and also in the Present Perfect (I have opened, you have eaten, etc.) Here are some helpful resources.
Online activities from the Realidades textbook
Book 2 Chapter 6B p. 331 (with the Present Perfect)
Book 3 Chapter 2A p. 79 (with Estar)
Online activities from the Exprésate textbook
Past participles used as adjectives 2.mp4Irregular past participles.mp4Past participles used as adjectives.mp444_past_participle_adject (1).mov3.3 - Past Participles as Adjectives in the Restaurant.flv
Self-correcting exercises
Grammar explanations with self-correcting exercises
Detailed grammar explanations with self-correcting exercises
Videos and interactive activities to learn Spanish online