Learn Italian: Guardo lo schermo. - I look at the screen.

In Italian, you usually do not need the subject pronoun (like io for "I") because the verb ending tells you who is doing the action. Guardo comes from the regular verb guardare (to look). Dropping the -are and adding -o tells us it is "I" doing the looking.

The English translation says "I look at", but where is the word for "at" in the Italian sentence?

The Italian verb guardare means "to look at" or "to watch" all by itself. You do not need to add an extra preposition for "at" after it. You just directly connect the verb to the object, saying essentially "I look the screen".

Why is the article lo used here instead of il for "the"?

Both lo and il mean "the" for masculine singular words. However, you must use lo when the following noun starts with an "s" followed by another consonant. Since schermo starts with "s" and "c", it requires lo.

Does the "sch" in schermo sound like the "sh" in the English word "shoe"?

No, in Italian, "ch" always makes a hard "k" sound. Therefore, the "sch" in schermo sounds like "sk", making the word sound like "SKER-mo".