In English, possession is most often indicated by use of an apostrophe ( ' ) + s ('s) with the noun, for example, "the professor's computer." But, while somewhat awkward in English, it can also be phrased as "the computer of the professor." Because there is no comparative form for the apostrophe ( ' ) + s in Portuguese, a form comparable to saying in English "the computer of the professor" is used. In written Brazilian Portuguese, the possessive adjective is most often always preceded by the definite article. In everyday spoken Brazilian Portuguese, the definite article is dropped and rarely used.
 

m-singular	f-singular	m-plural	f-plural	English
o meu	a minha	os meus	as minhas	my/mine (polite/formal)
meu	minha	meu	minhas	my/mine (informal)
o teu (p)	a tua	os teus	as tuas	your/yours (familiar singular)
o seu	a sua	os seus	as suas	his/her/hers/its/your/yours (polite/formal)
seu	sua	seus	suas	his/her/hers/its/your/yours (informal)
o nosso	a nossa	os nossos	as nossas	our/ours  (polite/formal)
nosso	nossa	nossos	nossas	our/ours  (informal)
a vosso (p)	a vossa	os vossos	as vossas	your/yours (formal familiar plural)
o seu	a sua	os seus	as suas	their/theirs/your/yours (polite/formal)
seu	sua	seus	suas	their/theirs/your/yours (informal)

(p) = Portugal

Possessive adjectives must always agree in both gender and number (singular or plural) with the accompanying noun — the possessor:

Onde ésta o nosso carro?
Where is our car?

O seu carro está lá mas os seus pneus foram roubados.
Your car is there but your tires have been stolen.