Learn Italian: Lo studente impara sottolineando e facendo uno schema. - The student learns by underlining and making an outline.

In Italian, the present gerund on its own (like sottolineando and facendo) often expresses the means or method of the main action. You don't need a preposition to say "by underlining" or "by making"—the gerund ending does that job all by itself.

Why is the gerund of fare facendo instead of "fando"?

Fare is an irregular verb that bases many of its forms on its original Latin root, facere. To make its gerund, you take that old root fac- and add the standard -endo ending, giving you facendo.

Why is it uno schema instead of un schema?

This is a quick reminder of an earlier rule: masculine nouns that start with "s" followed by another consonant require the article uno instead of un. Since schema starts with "sch", it takes uno.

How do we know who is underlining and making the outline?

When you use a gerund like this to show how an action is done, it must share the same subject as the main verb. Because lo studente is the subject of impara (learns), it is automatically understood that the student is also the one doing the underlining and outlining.