Possessive Adjectives:

(when the adjective is used reflexively, it "bends back (re-flecto) onto the subject. Note that the subject of the verb must be the same as the person indicated with the possessive adjective.

Also note the vagaries of the third person. Very tricky.

1st person:

singular:
meus, -a, -um (my, my own)

Librum meum legit. "He is reading my book"
Librum meum lego. "I am reading my own book."

plural:
noster, nostra, nostrum (our, our own)

Librum nostrum legit. "He is reading our book"
Librum nostrum legimus. "We are reading our own book."

2nd person:

singular:
tuus, -a, -um (your, your own)

Librum tuum legit. "He is reading your book"
Librum tuum legis. "You are you reading your own book.

plural:
vester, vestra, vestrum (your, your own)

3rd person: this is tricky!

singular:
eius (his, her, its)
Librum eius legit. "He is reading his (someone else's) book."

suus, -a, -um (his own or her own)
Librum suum legit. "He is reading his own book."

plural:
eorum, earum (their)
Librum eorum legit. "He is reading their (some other people's) book."

suus, -a, -um (his own or her own)
Librum suum legunt. "They are reading their own book."