Hello,
I’m very new to ardour and so my question shouldn’t take only to answer. I created a number of new tracks with the intention of making layered guitar tracks to a main guitar track. Unfortunately, I’m not used to the grouping automation, and added them to new group ‘guitar’, and now when I arm one of the tracks automation arms all of them, making it impossible to layer different takes as I had intended originally.
here is a screenshot
That is expected behavior by default. See here:
Paying special attention to activating/deactivating groups and overriding groups as these are common operations when working with groups. You may also want to look at shared properties as well to understand what all the checkboxes mean when creating the group.
Hello!
It’s hard to know exactly what you’re main problem is.
The term “automation” has to do with something else, so you might(?) be confusing the term with something else. 
But you can disable group-arming by deselecting this area for a given group:
Access this right-side panel by using shift-L (or clicking the button at the top circled there in green), then selecting “Track & Bus Groups” from the drop-down menu. 
-J
