To activate Gmail Tasks, you will have to go to Settings/Labs in your Gmail account and right at the top you will find the Tasks module. Just click ‘Enable’ and then you’re ready to go. If you go back to your Inbox now, under the Contacts tab you will find a Tasks link. When you click on this link, a lightweight Tasks module will appear on the bottom right corner of the screen, or pop out in a separate window, just like with Gmail Chat.
From here on, it’s pretty straightforward. You can add tasks and reorder them, and of course, cross out the completed ones. But the killer feature is that Gmail Tasks allows you to convert emails into tasks, in a remotely similar way to Apple’s Mail app on Mac OSX. In Gmail, you can select one or more messages, then go to More Actions> Add to Tasks and tasks are created out of your emails. For heavyweight users, keyboard shortcuts are also available.
However, its not yet a perfect feature. Even though you can add a due date for each task, this date doesn’t get automatically added to your Google Calendar and no such option is available. Also, there isn’t any option to share or email your tasks lists – like you can do with your calendars.