When do you know that this object is a direct object or indirect object.

Question

Céline Pickard · Accepted Answer

Bonjour Amanda Afia,
direct object: ask the question ‘qui, quoi’ (who, what)

J’aime Marie = I love Marie
J’aime qui = I love who → Marie
 
Je mange une pomme = I eat an apple
Je mange quoi = I eat what → une pomme
 
Je t’aime = I love you
J’aime qui = I love who → t’
 
Je donne mes clés = I give my keys
Je donne quoi = I give what → my keys

Indirect Object: ask the question ‘à qui/quoi – de qui/quoi’ (to whom/what – of whom/what)

Je donne mes clés à ma soeur = I give my keys to my sister
Je donne mes clés à qui = I give my keys to whom → ma soeur
 
Je lui donne mes clés = I give my keys to her
Je donne mes clés à qui = I give my keys to whom →lui
 
Je t’en offre = I offer some to you
J’en offre à qui = I offer some to whom → t’ / you

See link for direct/indirect object pronouns: direct-indirect-object-pronouns
I hope this is helpful.
Bonne journée!