You just need to change the word order for yes and no questions: -He is here. => Is he here? -They could do that. => They could do that? -I am using a computer. => Am I using a computer? -You have been to Australia. => Have you been to Australia? The only complication here is that 'do', 'does' and 'did' are usually omitted when not compulsory. When asking questions, you can't do this. You have to un-omit 'do' first (transferring the tense or conjugation to 'do' if necessary) before changing the word order. -I did that. => Did I do that? -I (do) see you. => I do see you. -She plays squash. = She does play squash. => Does she play squash? -They went there. = They did go there. => Did they go there? 'Do' was not compulsory in English until at least as recently as Shakespearean English, so it would have been perfectly correct to say "See I you?" or "Plays she squash?" (not that squash was invented". Unfortunately this is not the case in modern English. Once you change the word order, you can also add question words to the front of the sentence. -Is he here? => Why is he here? -Did I do that? => When/Why/How (etc.) did I do that? -Does she play squash? => When does she play squash? It's important to remember that you change the word order for questions, but NOT for statements. Ex. -"I don't know why did she do that." and "Why she did that?" are both incorrect. You have to say "I don't know why she did that." and "Why did she do that?" -"I will go when is it dark outside." and "It is dark outside?" are both incorrect sentences (see the next paragraph about what the latter could mean in spoken language). You have to say "I will go when it is dark outside." and "Is it dark outside?"

Part two: There are some exceptions you might see in the spoken language. If a statement is written with a question mark, it's not really a question as much as a surprised inference and the question mark just indicates the rising intonation at the end of the sentence. For example, if someone implies that it's dark outside and I thought it was light, I might say "It's dark outside?". I'm not actually asking if it's dark outside, I'm just indicating my surprise. Someone might confirm my inference with "yeah", especially if I sound uncertain, but that's not really necessary. "Are you..." is often omitted before questions in the present continuous. Ex. "Are you using a computer?" might be abbreviated to "You using a computer?" or "Using a computer?". This is really slang-ish and not proper, but it's very common. By the way, never start a question with "how to" or "what to". You could say "I don't know how to do that." or "I need to know what to do.", but you can't just say "How to do that?" or "What to do?". In novels you might see people use this form when they're thinking in self-contemplation, but this sounds very old-fashioned and something you'd only expect to find in a book, and it was never used to ask someone else a question in the first place. You might also see something like "How to ask any question in English" as the title of an article, but it is neither a full sentence nor a question. I would expect that article to explain how to ask questions in English rather than ask about it. The title of this page should be "How do you ask any question in English?"