Every HubSpot portal with deals has at least one pipeline. Each pipeline holds a list of stages in order, ending with a closed won and a closed lost stage. Each stage has a win probability that feeds weighted pipeline amounts, and you can make certain properties required when a deal moves into a stage. Depending on your subscription, you can create more than one pipeline, for example one for new business and one for renewals.
The pipeline is where sales process becomes data. Board views show deals as cards moving across stages. Reports use stage entry dates to measure conversion between stages and time spent in each. Forecasts and weighted pipeline depend on the stage each deal sits in. If stages do not match how the team really sells, every one of those numbers is off.
Good stages describe something the buyer has done or agreed to, not something the rep hopes will happen. "Demo completed" and "Proposal sent" are checkable. "Interested" is not. Each stage should have a short written exit criterion, so two reps would put the same deal in the same place.
Keep the pipeline short enough that every stage gets used. Stages that no deal ever enters, or that most deals skip, are a sign the pipeline was designed in a meeting rather than taken from real deals. Review pipelines at least once a year, and before you change stages, check which workflows, reports and forecasts rely on them.