Invisalign Attachments Procedure Video
Invisalign Attachments are required to allow aligners to get a better grip on the teeth. Sometimes they are used to directly move teeth, while other times, they are used as anchors to help move other teeth in the arch.
They are made of a tooth-coloured material that will stay on your teeth for the course of your treatment. They are not very noticeable, and definitely much more aesthetic than braces.
Here's a video that describes the entire attachments process: