A deal is a single opportunity you're working. The pipeline is the visual board that shows every open deal by stage, so your whole team can see where things stand at a glance.
The pipeline is a Kanban board: drag a deal from one stage to the next as it progresses. Each stage is one of three kinds — open, won, or lost — so moving a deal into a "won" or "lost" stage closes it out. The board also shows the number of open deals and their total value per stage, giving you an instant read on your pipeline's health.
You can also switch to a list view of deals, and open any deal's full record to see and edit everything about it.