Learn Italian: Mia sorella sposa un ragazzo italiano. - My sister is marrying an Italian boy.

In Italian, you usually put a definite article before a possessive, as in la mia macchina (my car). However, singular family members are the big exception! With words like sorella, you drop the article and just say mia sorella.

Why does the Italian use sposa (marries) instead of a form of 'is marrying'?

Italian frequently uses the simple present tense to talk about future plans or ongoing actions. While Italian does have a present continuous tense, the simple present is very common and natural for statements like this.

Since we are learning about the particle si, why doesn't this sentence use si sposa?

That is a great question! When you say exactly who someone is marrying, you use the regular verb sposare followed directly by the person (sposa un ragazzo italiano). You only use the reflexive si sposa when talking about getting married in general (mia sorella si sposa) or if you use the preposition con (si sposa con un ragazzo italiano).

Why isn't italiano capitalized?

In English, nationalities are always capitalized. In Italian, they are written in lowercase when used as adjectives describing nouns, like un ragazzo italiano.