La and el are the definite articles in Spanish. They are singular, and la is feminine, el is masculine.
Las and los are definite articles but they are plural. Las is feminine, Los is masculine.
They mean the word 'the'.
Un and una are indefinite articles, and they are singular. Un is masculine, una is feminine. They mean the words a, an, or one in English.
Unas and unos are indefinite. They are plural, and the mean some, about, or few.
