For editing offline, I recommend you use XAMPP http://www.apachefriends.org/en/xampp.html which is extremely easy to set up - in fact, you just need to run an installer! It is a package that includes the Apache server, PHP and mySQL and other stuff you need.

It turns our comp into a server and so you can test out your PHP files. XAMPP will give you appropriate instructions during and after installation.

Remember that when you are editing offline, don't use absolute pathnames, otherwise you will need to change all you links when, if, you upload it to a server.

PS As you get more experienced, you will probably want to try and do the installation process by yourself, as it gives you a lot more control.

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