Projects are a way to organise time entries under a specific contact. Just hit the hash # key (SHIFT + 3) when you’re creating your entry and it will drop down a list of existing Projects, or allow you to create new ones. You can only associate one Project per entry.
You can generate goals and filter reports based on Projects.
You can manage your Projects at any time by visiting the Projects tab - you can create default hourly rates for projects and even pin them like Contacts!