access-specifier return-type method-name(parameters)
{
}

Simple example of a method:

public void sayHello()
{
System.out.println("Hello Tom !!");
}

A method can have one or more parameters. 
Example consider a method to add two numbers

public void add(int num1,int num2)
{
int sum=num1+num2;
}

A method with return type void means that the method will not return anything, but if a method requires to return back something it will have return type other than void.

And a point to remember here is that it will require to include a return statement at the end of the method.
Or in simple words.

 IF A METHOD RETURN SOMETHING, LAST STATEMENT IN THE METHOD WILL be the return statement.

Example of a method with return statement

public int square(int num)
{
int i=num*num;
return i;
}