Learn Russian: Я устал и хочу помолчать. - I am tired and want to be quiet for a bit.

The prefix по- turns the imperfective verb молчать (to be silent) into the perfective помолчать. This specific prefix adds the meaning of doing an action for a short, limited amount of time. So, the speaker doesn't want to take a vow of silence, they just want to be quiet for a little bit.

Why use a perfective verb (помолчать) after хочу? Don't we usually use imperfective for ongoing states like being quiet?

You use the perfective here because you are expressing a desire for a specific, one-time action with a clear time limit. The по- prefix packages the state of being quiet into a single, completed chunk of time, making it perfective. If you used the imperfective молчать, it would sound more like a general, open-ended desire to just not speak.

I am female. Do I need to change the word устал?

Yes. Even though tired acts like an adjective in English, устал is actually the past tense masculine form of the verb устать (to get tired). Because it is a past tense verb, it must agree with the gender of the speaker. A female speaker must say Я устала.

Wait, if устал is in the past tense, why does it translate to I AM tired right now?