请【qǐng】

请 in front of a verb makes it a polite request. It comes first, before anything else in the sentence.

Unlike English "please", 请 cannot be dropped in at the end. Zuò坐qǐng请 is wrong.

请问 to open a question

Before asking a stranger anything, 请问 is the standard opener.

Softening further

一下 and 一点儿 after the verb take the edge off a request, and 吧 at the end makes it an invitation rather than an instruction.

请 with a person

请 plus someone plus a verb means asking them to do something.

请 as "to treat"

A separate use: paying for someone's meal.

请客 is the noun-like version – 谁请客 asks who is paying.