Adding a javascript file to the “blank” template in magento

[username33]

I'm using Magento 1.5 (CE) and I'm slowly getting my head around it (how confusing is this piece of software?).I want to add a js file to all my pages, but I'm not sure what i need to edit. I have created a file called \[code\]app.js\[/code\] located in \[code\]/skin/frontend/default/blank/js\[/code\] how do i add this file to all my templates?