In the track view pane just move your cursor to the track you want to automate and right click. There you will see various options one of which is arm track for automation. Just go down and click on that option and your automation button should now be enabled.
If you have your midi project loaded it should just be a matter of selecting the track you wish to automate, Hit the automation button and your off.
If the project is blank then the automation recording will not work.