Learn Italian: Marco compra un regalo per lei. - Marco is buying a gift for her.

In Italian, after a preposition like per (for), you must use a "tonic" (or stressed) pronoun. For "her", this pronoun is lei. You only use words like la or le when the pronoun is interacting directly with a verb, without a preposition in between.

Could per lei also mean "for you" in a formal situation?

Yes! If you are speaking to someone using the formal "you", per Lei means "for you". It is often capitalized when written down to make this clear, but in spoken Italian, only the context tells you if it means "for her" or "for you (formal)".

Does compra mean "buys" or "is buying"?

It can mean both! The Italian present tense covers both the simple present ("Marco buys") and the present continuous ("Marco is buying"). You don't need a separate verb form to say "is buying".

Why is it un regalo and not uno regalo?

Regalo is a masculine noun starting with a regular consonant (r). You use un for most masculine words. You only use uno for masculine words starting with an "s" followed by a consonant (like uno studente), a "z" (like uno zaino), or a few other specific sounds.