The Google app is beginning to test screenshot editing tools for some users allowing them to make a handful of minor changes to a screenshot prior to sending it off to whoever they want to share it with. The editing tools are not showing up for all users and only seem to be applicable to screenshots that are taken within the Google app, and it appears that you need to be on the most recent version of the Google app beta for these options to show up.
The way that the feature works is if you're inside the Google app and you snap a screenshot, instead of disappearing into the status bar like screenshots do for any other location in the system, the Google app expands the share menu and in it should be the included options for cropping and drawing on your screenshot if there is any reason why would you need or want to do so. The cropping is fairly basic and works just like the crop feature in Google Photos. As for the drawing feature, you'll have an arrangement of different colors at your disposal, but there are no options for different pen tips or tip sizes so what you're getting is a simple drawing tool for perhaps making a quick note or highlight on a specific part of the image. Those who need something a bit more varied will want to edit their screenshots elsewhere.
While the drawing is fairly simple and there aren't a lot of options included with it, it's still possible to mess something up so if users don't get things right the first time they can tap a button to reverse what they've already drawn and start over, which should save the time and hassle of having to re-open the image and edit after the fact. In addition, once any edits are completed Google brings the user back to the share menu to complete the overall sharing of the screenshot. Whether or not Google includes these editing options for other apps is unclear but there is always a possibility they could roll it out to other apps.