The idea
The new student
A new student joins your class. Will they like cricket or football?
You don't know them yet. But you can look at the 3 students most like them (same age, same hostel, same hobbies) and go with what most of those 3 like.
To guess about someone new, find the most similar people you already know and take a vote.
That's the entire idea of k-Nearest Neighbours (KNN). k is how many neighbours you ask.