Google completely abandoned its standalone Tasks service for a long time and built reminder functionality into Inbox (RIP), Keep, and the Assistant instead. Last year, however, a Google Tasks redesign surfaced out of nowhere, complete with Gmail integration on the web. Now, the latest Gmail app update brings this functionality to Android.
To add an email to Google Tasks, you simply open its overflow menu (the three-dot menu) and click "Add to Tasks." A toast message at the bottom of the screen will tell you that you've successfully created said task, and you can even jump right into the Tasks app by pressing "View." If you don't have it installed, clicking on "Add to Tasks" takes you to the app's Play Store listing instead.
Left: "Add to Tasks" at the bottom of the overflow menu is new. Middle: A toast acknowledges the new task. Right: Clicking on "View" leads you into the Tasks app.
While I welcome the ability to assign tasks to emails after this feature disappeared along with Inbox, I'm missing the latter's simplicity. You could add notes and view to-dos right inside your inbox there, while you need to jump back and forth between Gmail and Tasks to get the same functionality – though I like the fact that you can annotate items there in far more detail than you used to be able to in Inbox.
If you'd like to try the new option for yourself, you need to be on the latest Gmail release (and you might need to wait a bit until the feature rolls out to you from Google's servers). You can find it on the Play Store through the widget below or sideload it over at APK Mirror.