Before you program in javascript you must learn HTML and know how to use it without Dream-weaver or any other similar programs. But lets say you have this prerequisite. You now have two options you...
Programmers use it to develop websites, by using JavaScript in websites developers will be able to change properties of objects without reloading page (client side)
You already have it inside your browser, you dont need anything else. So a simple notepad document will do the trick. Simply put your javascript code between the javascript tags and save it as...
JavaScript is pre installed {in every web browser} and so is Java {if it was bought before 2008} all you have to do to use it is go to notepad [I use Notepad++] type all the HTML standard...
Java script can be used to automate simple tasks that may be repetitive to computer users. You can also use java script in web pages to have interaction with the user.