What exactly are constructors needed for in java?

Question

pls I'm a beginner in java. l've been trying to understand the need for constructors when you still create objects in the main method and have instance variable in the class.?
pls what exactly are constructors for and what is difference between an variable and a parameter?
thanks

Answer 1

https://en.m.wikipedia.org/wiki/Constructor_(object-oriented_programming)

Answer 2

What is the difference between an instance variable and a parameter with respect to a constructor?