The word "possessive" might be a bit misleading. Yes, we use possessives for things that we actually possess, but we also use them for relationships. When I say "my sister" it's not because I own her, but because I'm defining the relationship between us. Here are some resources for you to explore this topic.
Online activities from the Exprésate textbook
Book 1 Chapter 5A p. 162 (Possessive adjectives)
Book 2 Chapter 5A p. 174 (Possessive pronouns)
 HOLT_EXPR_SATE_LEVEL_1_DISC_1.Title41 Possessive adjectives.avi
HOLT_EXPR_SATE_LEVEL_1_DISC_1.Title41 Possessive adjectives.avi Possessive adjectives.mp4
Possessive adjectives.mp4 A05 Possessive adjectives.wmv
A05 Possessive adjectives.wmv 4.11 - Possessive Pronouns in the Lost & Found.flv
4.11 - Possessive Pronouns in the Lost & Found.flv 4.9 - Possessive Adjectives and Body Parts in the Doctor_s Office.flv
4.9 - Possessive Adjectives and Body Parts in the Doctor_s Office.flv Possessives sample video.avi
Possessives sample video.aviDetailed grammar explanations with self-correcting exercises
Excellent grammar explanations with video
Music videos to help you learn!