In Portuguese every noun is either masculine or feminine — not just people, but plates, tables and cities too. The gender decides which word you use for the and a:

	Masculine	Feminine
the	o prato	a mesa
a / an	um prato	uma mesa
the (plural)	os pratos	as mesas
some	uns pratos	umas mesas

Prato is a plate, mesa a table; you'll also meet copo (glass), garrafa (bottle) and livro (book). Most nouns that end in a vowel just add -s in the plural: o prato → os pratos, a mesa → as mesas.

You've already met the article in front of names: a Marina, o Marcos.