Learn Spanish (Latin America): Hay un micrófono en el maletín; no lo abras. - There is a microphone in the briefcase; do not open it.

When you give a negative command in Spanish (telling someone not to do something), object pronouns like lo must be placed immediately before the conjugated verb. You cannot attach them to the end of the word.

Could I attach the pronoun and say no abraslo instead?

No. Pronouns can only be attached to the end of affirmative commands (like ábrelo - open it), infinitives, and "-ing" words. For all negative commands, the pronoun must stand alone before the verb.

Why does the verb end in "-as" (abras) instead of "-es" (abres) or "-e" (abre)?

To form a negative informal command (telling someone you address as tú not to do something), Spanish uses a different set of endings. For "-er" and "-ir" verbs like abrir, the ending changes to -as. So, while "you open" is abres, "don't open" becomes no abras.

What exactly does lo refer to here?

lo is a masculine singular pronoun meaning "it". In this sentence, it replaces el maletín (the briefcase). Even though un micrófono is also masculine, common sense tells us you shouldn't open the briefcase, not the microphone!