Short Version

1. Select a sentence in any application
2. Trigger an action (either by the menu bar or keyboard shortcut)
3. The text gets replaced with the result

Detailed Steps

1. Open any text editor for example apple notes app
2. Write a sentence with some errors, for example:

Excited to announce our new prodct launch! Check out our revolushunary gadget, now availble in stores near you. Its going to change the way you do things forevr! 

1. Select that sentence as you would copy and paste it
2. Trigger an action, for example: Fix Grammar & Spelling
3. Wait for loading
   1. A loading indicator should appear near your mouse cursor
   2. Keep your editor with the selected text open and focused
4. Your selected text will be replaced with the corrected version
   1. You should see that some errors are fixed (e.g. prodct → product)