Ok, so you know how when we talk in sentences, we usually start with the subject first and then say what the subject is doing? Like, "I am eating a banana." The subject is "I" and the rest of the sentence is telling you what "I" am doing.
Well, sometimes when we want to ask a question, we switch the order around. So instead of saying "You are eating a banana," we might ask "Are you eating a banana?" We moved the verb "are" to the beginning of the sentence to make it a question.
Wh-fronting is when we do this with other special words like "who," "what," "when," "where," "why," and "how." So instead of saying "He went to the store," we might ask "Where did he go?" We moved the word "where" to the beginning of the sentence to ask a question.
So basically, wh-fronting is when we move special question words to the beginning of a sentence to ask a question.