'Find' part will change based on the underlying data. So if you click Add to autotag on an URL, you will get view tailored to URL.

Similarly clicking Add to autotag on an Office document will show this:

Lets take a closer look at url example. Most of you are probably familiar with GMail. When you are using it, ManicTime will show urls similar to this one on the Documents timeline
https://mail.google.com/mail/u/0/#inbox

So the question is, how can you set up an autotag for GMail? When you right click on one of the GMail urls in ManicTime, you get this window

The first option is no good. You don't want every visit to google.com (search, email....) result in Mail autotag.
In this case you need to pick the second option.

Lets take a look at another example, lets say you want to autotag Skype as 'Communication'. You can do this by clicking on Applications timeline to select it. Then in the bottom right, you need to right click on Skype and choose Add to autotag.

Add to autotag window is helpful when adding rules, but sometimes you need to add your own more complex rules. Let's say that you want to autotag all activities where you've used Firefox and there is a word 'manictime' in title. Click on Applications timeline to select it, then in the filter at the bottom write:
'group:firefox manictime'
Then click on the down arrow on the right side and choose Add to autotag to add current filter to autotag.