A hands-on lab is an online learning environment along with a set of instructions to walk you through a live, real world, and scenario-based use case. In a lab you have access to the actual environment you want to learn about, not a simulation or demo environment. You can access the lab environment from anywhere on the Internet using a standard browser.
Most labs require credits to access, but there are a number of free introductory labs available as well.
Qwiklabs does not provide any official certificate regarding lab completion. However, you can earn badges by completing Qwiklabs Quests.