Questions & Answers about Пожалуйста, налей мне чай.
Here пожалуйста means please.
It makes the request more polite. Russian often uses the imperative together with пожалуйста for normal polite requests:
- Скажите, пожалуйста... = Please tell me...
- Дайте, пожалуйста... = Please give me...
So Пожалуйста, налей мне чай is a polite request, not a harsh command.
Налить is the infinitive, meaning to pour.
Налей is the imperative form, meaning pour! or please pour.
So:
- налить = to pour
- налей = pour!
In this sentence, the speaker is asking someone to do the action, so Russian uses the imperative: налей.