Providing timely feedback to students is important, yet time-consuming. One way to be efficient with feedback is to provide voice feedback with Mote as previously mentioned. Another method is to set up canned feedback in Preferences of Google Docs. To do this, go to Tools > Preferences and choose the Substitution tab. You will notice that Google already has some automatic substitution listed and you can continue to add some of your own. Just type in your personal abbreviation for a canned response and it will appear in the document when you use that abbreviation. You and the students can also use abbreviations with personal papers and notes.
This can also be done in Google Slides, however, you will need to repeat these procedures for Google Slides. (The canned feedback will not transfer.)
In order to highlight the changes to the students in green, you can change from Editing mode to Suggesting mode for Google Docs. Giving feedback in suggesting mode also makes your edits pop up as comments. The Suggesting mode feature is not available in Google Slides.