Static variables and methods belong to the class and not instance, although you can refer them from an instance reference. Usually, you use the Class name to access them.
If a method is declared as static, you don't need the object's instance in which it is defined to invoke it. Now, you might want to know when could such a situation arise? Consider the main method of java
public static void main(String[] args)
Why is it declared static? It's because in order to start your program this method should begin execution. And, since the program hasn't initialized there is no way you could create an instance of the class in which it is declared. Therefore, you are required to declare the class as public. And, this static method gets called when the class is loaded in memory through
java YourClassName
Besides this, static methods are used to modify static variables. They cannot manipulate non-static instance variables.
Also, be aware, that static holds a different meaning in another language like C.