Which is correct – “I can have an apple?” or “Can I have an apple?”
The order (sequence) of words in an English sentence is often different from the word order of the same sentence in other languages. The word order in a question is even a little more difficult.
This picture may help you. It’s called the “Question Hand”. To make a Yes/No question, start at the pointer finger. The “X word” can be an auxiliary (helping) verb or the only verb in the question.
Examples: Did (x word) he (subject) eat (main verb) dinner with you? Is she coming home? Can I have an apple? Are you okay?
To make other informational (open-ended) questions, start with the thumb.
Examples: Where (question word) do (x word) you (subject) live (main verb)?
What time did you get home?
And here is some more explanation, plus many more practice exercises.