How to text on mac Yosemite?

I've downloaded Yosemite, updated my phone to ios8.1, and went to settings>messages< Text Message Forwarding and clicked my macbook but a pop up comes up and says "Enter the code shown on your Mac to allow iPhone text messages to also be received on your macbook" But no code comes up on my mac? Please help!

Added (1). Every time i press my macbook, it opens up messages on my computer but no code?

You'd have to use Messages to text & this is also where you'd find the code when presented.