Breakdown of Он поступает в институт.
он
he / it (for a masculine noun) / it (for a neuter noun)
в
in / to (direction)
институт
institute
поступать
to act; to enrol
Questions & Answers about Он поступает в институт.
Why do we use в институт (Accusative) here instead of в институте (Prepositional)?
Even though the English translation says 'at the institute', the Russian verb поступает implies a direction or a transition into a new place. When indicating direction, the preposition в takes the Accusative case. If we used the Prepositional case (в институте), it would mean he is already physically inside the building performing an action.
Since институт is in the Accusative case, why didn't its ending change?
Институт is a masculine, inanimate noun (a non-living thing). In Russian, the Accusative form for inanimate masculine nouns looks exactly the same as their Nominative (dictionary) form.
Does поступает mean he has already been accepted to the institute?
Not necessarily. Поступает is an imperfective verb, which focuses on the ongoing process. In Russian, this often means he is currently applying or taking entrance exams. To say he successfully got in, you would use the past tense of the perfective verb: Он поступил в институт.
How could I use the current lesson's grammar (чтобы + infinitive) with this sentence?
You can easily attach a чтобы (in order to) clause to explain his purpose for enrolling. For example, you could say: Он поступает в институт, чтобы стать врачом (He is enrolling at the institute in order to become a doctor).