吗 (ma) is the easiest way to ask a question in Chinese. Put it at the end of a statement and the statement becomes a yes/no question. Nothing else in the sentence moves. It is one of the first grammar points of HSK 1.
Statement + 吗？
Unlike English, Chinese does not change the word order to ask a question, and there is no word like "do" or "does". Take a normal sentence such as 你是学生 (you are a student), add 吗 at the end, and it becomes "Are you a student?". 吗 is said with a light, neutral tone.
Chinese has no single word for "yes" or "no". To answer, repeat the main verb or adjective from the question: 有 or 没有, 会 or 不会, 想 or 不想. For questions with 是, answer 是 or 不是.
With adjectives, 很 is usually left out of the question and comes back in the answer: 你忙吗？ is answered with 我很忙. If someone tells you something surprising, 是吗？ on its own means "Really?".
Only use 吗 when the answer is yes or no. If the question already has a question word such as 什么, 谁, 哪儿 or 几, it is already a question, so do not add 吗. 你叫什么名字吗？ is wrong; say 你叫什么名字？.
The same goes for the "verb + 不 + verb" question, such as 去不去. It asks the same thing as 吗, so you use one or the other, never both.
You can also add 吗 to a negative sentence. This often shows a little surprise, like "Aren't you...?" in English.
Be careful when you answer. In Chinese you agree or disagree with what the other person said, so 对 means "right, I'm not". English speakers often get this the wrong way round.
Every example on this page uses only words up to HSK 1. Paste your own sentences into the level checker to see which words, if any, are above your level.