Gmail labs is a place for testing experimental features that are not quite ready to roll out as a standard feature. These things may change, break or disappear at any time. To activate the to-do list also known as Tasks:

1. Click on settings within gmail
2. Click on Labs
3. Enable Tasks
4. Click Save Changes near the bottom of the page

On the left hand side of the page will be a Tasks link. When you click on it you a to-do list will appear on the right – click anywhere in the list and start typing to add a task. So Simple. Have fun.