Applicant day

I have received an offer from Manchester and am currently undecided to if i want to study there. I recently got in contact with the university to inquire about the course. They suggested for more information go to the applicant day.

Therefore I was wondering what are applicant days like and how useful/necessary are they in general.

There's no specific criteria for what the day will involve. Usually you'll have a talk about the course and then some or all of:
Informal chats with staff
Informal chats with students
Tours of facilities
Tours of library
Tour of accommodation
Student union/student life talk/tour