请问 (qǐng wèn) is a polite formula used to start a question, like 'excuse me, may I ask...'. It's more formal and respectful than 问 (wèn 'to ask') and is not an apology like 对不起 (duì bu qǐ) or 不好意思 (bù hǎo yì si). Use it when you need to ask for information from a stranger or in a service setting.