In English, a WH-word or phrase (for example, who, what, whose computer, which student, etc.) must occur at the beginning of a clause. Therefore, the WH-word or phrase appears to have "moved" to the beginning of the clause from some other position in the sentence where it would otherwise appear if it were not a WH-word or phrase.
When a WH-word or phrase represents the subject of the sentence, it has not moved from any other position within the sentence. In the following question, the WH-word who is the subject of the sentence, so the question reflects the normal SVO word order.
Who (S) translated (V) the sentence (O) for the student?
In the next question, who represents the object of the verb help. (In more formal English, some people would use whom, rather than who, as an object.) The line (____) indicates the position after help from which who has moved to the beginning of the sentence.
Who (O) did (V) the student (S) help (V) ____ with the translation?
In the next sentence, who has moved even further, from a position in a separate clause (…the teacher helped ____ with the translation) that follows the main verb say.
Who (O) did (V) the student (S) say (V) the teacher (S) helped (V) ____ with the translation?
The above three sentences reflect SVO, OVSV, and OVSVSV word orders, respectively. These sentences illustrate that the further a sentence element such as a WH-word has moved to the beginning of a sentence, the greater the deviation from simple SVO word order and the more complex the sentence is with respect to the relationships among the subjects, verbs, and objects it contains. For example, in the third sentence, the first O is the object of the third V!