Searching
There are two search functions.
Quick search
Just enter text into the quick search box atop. Streamtuner2 will instantly highlight any matches in the current stations view. If you switch tabs, just click the glass icon to reapply the highlighting.
Search window
You can get to the search dialog via Edit ▸ Find or Ctrl+F. Centrally to this dialog is the text field, where you can specify the phrase to scan for.
It either will search in all channels, or just the last active channel/service.
Then there are two search variants. You mostly want to use the live Server search. It passes your search terms to the actual directory services, and loads the most recent data into a result list. This might take a few seconds. And it's not implemented for all channel plugins. (Some websites/APIs don't have a search.)
While Cache find would just look up entries in your already downloaded channel/genre lists. This is sufficient when you're just looking for something previously seen/listened to.