When do I need to make past participle agreements?

You should make the past participle agree with its subject in the following cases:
1) It is a past participle of an ordinary verb conjugated with ETRE E.g. je suis allée (JE = SUBJECT)
2) It is a past participle of a verb in the PASSIVE E.g. elle a été renversée par une voiture (ELLE = SUBJECT)
3) It is a past participle of a verb conjugated with AVOIR with a DIRECT OBJECT preceding the verb (Proceeding Direct Object) E.g. voici les tables que j'ai commandées (TABLES = SUBJECT, FEM. PLURAL)
4) It is a PROMINAL VERB - one that uses 'se' at the start-> Reflexive -> Reciprocal