The Team Leaderboard tab shows the teams in the event (e.g. Team XYZ in the NYC Marathon) and the Top Individuals tab shows individuals regardless of what team they're on.
Some events may have one or both of these tabs disabled. There are also various controls for how these are organized. For example, you may choose to include or exclude Offline Donations from being taken into account in the leaderboard standings, if your event allows teams to add those at all.