gustabo
Hit the "W" to Write the automation, R is "Read"
Brando is correct. W is for Write and R is for Read. Sorry for any confusion.
Click the W and move the pedal to create the automation. If you leave the R button on it only means it will be reading while writing. This way you can make minor changes while write is enabled so when you let go of the pedal it will snap back to previous automation you have done previous.
You can also leave Read off until you are finished with automation. I use this feature all the time and im not sure why I left bogus info in my first comment. there are also 3 different automation modes (Overwrite, Touch, and Latch.)
Read here to see what each one does (but for all intent, overwrite is the way to go),
https://www.cakewalk.com/Documentation?product=SONAR%20X3&language=3&help=Automation.04.html After Automation is complete you can go back in to a lane and fine tune it.