To add Gmail Labs features, log in to your Gmail account on the Web.
Click on the Settings link on the upper right-hand corner of the screen. From there, click on Labs.
Select enable next to each feature you wish to use, and then hit the save changes button on the bottom of the page to start using your new features.
If you're having trouble and a Gmail Labs feature breaks, you can temporarily disable all Gmail Labs features by going to the Labs "escape hatch."