"I need it."
Hi garpet! "Χρειάζομαι" is a deponent verb, i.e. a verb whose voice is active but looks like it's passive. Deponent verbs do not also have another form in active voice. Verbs in their passive voice forms, as well as deponent verbs, end in "-μαι".
You know that the subject is "I" because "χρειάζομαι" is first person singular. If the subject was second person singular, then you would see "χρειάζεσαι", if it was third person singular, you would see "χρειάζεται", etc. Look up conjugation of "χρειάζομαι" for more!