The ex4 file has already been compiled therefore it does not need to be opened in your metaeditor. Right click on metatrader and open file extensions - double click on experts - and then double on indicators - then drag the ex4 file in there - if your metatrader is open you will need to close it before it appears in your indicators list inside the program.
Try that

Gravity,
In metaeditor, go to file and click open - then locate the file you wish to compile on your computer - I usually save my mq4s - to my desktop at first so I can find them. Once you open the file in metaeditor you should be able to compile it and it will put the new file on your desktop.

Gravity,
I just saw your message - sorry. The files with mq4 extension need to be downloaded into metaeditor and compiled. This will convert them to the ex4 extension - where you can just copy and paste into the indicator file within metatrader. The tpl extension is a template file and that needs to be dropped into the template folder with metatrader.
Hope this helps,
JAWPIP