Let's piece this sentence together. The Spanish word for "I" is yo.
The next word is "need." The conjugation in present tense of "need" for the subject yo is necesito.
Finally, we have "to study." This will be an infinitive in Spanish. The infinitive meaning "to study" is estudiar.
Answer:
Yo necesito estudiar.
The other options are:
Yo necesito estudio. - "I need study."
Yo necesito tú estudia. - "I need your study."
Yo necesita estudiar. - This uses the wrong conjugation of necesitar.
