(OT, but trying to be helpful for non-native speakers) their - possessive/ownership. "Their dog bit me!" "Their car is a mess!" there - place/position. "Put t

(OT, but trying to be helpful for non-native speakers) their - possessive/ownership. "Their dog bit me!" "Their car is a mess!" there - place/position. "Put the toys over there." they're - contraction of "they are". "They are my best friends!" == "They're my best friends!"