First post and first project! Need help!

Hi everyone!

OK so as mentioned this is my first post and first project! What I'm trying to accomplish with this project is a IR Motion Detector that transmits via a 2 way radio. I'm pretty sure I get how most of it goes together except how to get the Arduino to send a signal via the radio. I would really appreciate some help from you much much more knowledgeable folks. Here is a video on YouTube that inspired this project. I essentially want the same thing.

It's a little hard to understand where the Arduino comes into the equation ?

What do you want the Arduino to do?

Well I thought I could use it to run my PIR and have it send the signal through the radio once the PIR picks up movement. In this fashion here :

Not the way to do this?