Order entries by "recently modified" date time in control panel Ok somebody ought to start asking the Totally Green questions, it may as well be me.  How do I show the date and time an entry was last manipulated in the control panel?

I produce video more than websites, though that is rapidly changing, and will so even more as the canvas becomes the new After Effects, so I am giving up and in and I'm going to ask all the questions total neophytes would, if it's okay with you people.  Eventually I'm gonna announce my first plug-in, pat myself on the back, and drink a shot.
Short answer is, you can't.

Long answer... Ian has some good advice, but the Post Date won't update automatically. Your best solution would be to update the Post Date every time you update something else in the entry. Then your Post Date will essentially represent your "last changed" date.

Bonus answer... If/when you do build your own plugin, you can look into building your own Element Type. (Just a fair warning... building a custom Element Type is a little more advanced.) When you're setting up your Element Type, you can define which columns appear in that "list" view. One of the native columns in every Craft DB table is "dateUpdated", which contains exactly the information you're looking for. Just output that as one of your columns, and voila!

There's no rush, I can wait answer... the ability to add custom, sortable columns to the entries (and users, assets, etc.) index pages is coming “Real Soon Now”™.