If you wish to add inbuilt java libraries to your program in order to use their functions, you will use the import statement. following is the syntax for the import statement:-
import java.lang.Math;
With the help of this statement, you can use the functions Math.sqrt(),Math.abs etc
Over here, Lang is a folder full of Java libraries and Math is just one file which allows you to use the functions associated with the object Math. if you wish to import multiple files from one same folder you can replace the name of the object by *. For example
import java.lang.*;
The above statement will allow you to use all the object within the package "lang".
Hope this helps