In Java, a package is a way to group related classes and interfaces together. A package can contain any number of classes, as well as other packages. The main purpose of a package is to provide a namespace for the classes and to prevent naming conflicts with classes in other packages.

To create a package, you need to include a package statement at the beginning of your Java file, followed by your class definition. The package statement should be the first line of code in your file, and should look something like this:

package com.example.mypackage;

This statement declares that the class in the file belongs to the "com.example.mypackage" package. You can choose any name for your package, but it is recommended to follow a convention of using a reversed domain name as the package name to avoid naming conflicts.

To use classes in a package from another package, you need to import the package using an import statement. For example, if you have a class called "MyClass" in the "com.example.mypackage" package, and you want to use it in another class called "MyOtherClass" in a different package, you can do the following:

package com.example.myotherpackage;

import com.example.mypackage.MyClass;

public class MyOtherClass {
    public static void main(String[] args) {
        MyClass myObject = new MyClass();
        myObject.doSomething();
    }
}

In this example, we import the "com.example.mypackage.MyClass" class using an import statement, and then create a new instance of the class and call its doSomething() method.

The Java standard library provides many packages that contain useful classes and interfaces, such as the java.util package for utility classes, the java.io package for input and output classes, and the java.net package for networking classes.