ENTER = to come or go into a particular place. ENTER is usually a transitive verb; therefore it has an object and is not used with the prepositions TO, INTO or IN; e.g.
INCORRECT: They entered into the building through the front door.
CORRECT: They entered the building through the front door.
INCORRECT: After entering into university, students make a lot of new friends.
CORRECT: After entering university, students make a lot of new friends.
INCORRECT: In the past it was unthinkable that a woman could enter in politics.
CORRECT: In the past it was unthinkable that a woman could enter politics.
NOTE-I: Don’t confuse this use with the phrasal verb ENTER INTO, which means ‘to start agreements, contracts or discussions with someone; e.g.
Today, eighteen-year olds are considered responsible enough to enter into contracts.
NOTE-II: ENTER can be used without an object; e.g.
They stopped talking as soon as they saw Sunita enter.