A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
Questions about the scope of Lifehacks SE such as "What questions are on-topic?", "What is a valid answer?", etc.
for questions about answers: how to answer, whether specific answers are appropriate, and so forth.
For questions about the behavior or usage of tags, which are keywords or labels that categorize and group your question with other, similar questions.
for questions dealing with moderator actions, pages, abilities or decisions.
For questions regarding the nature of a "question" on StackExchange sites; e.g. how to ask, whether specific questions are appropriate, etc.
For questions about the flagging process, how flags are handled, etc.
For questions about the process of editing, how edits work, and other general inquiries about the edit system.
for questions specific to down-votes, the community's way of telling peers that their content can be improved. Down-votes on meta site have different meanings.
the primary way users gain reputation, and also how many items are sorted to the top.