If you want multiple Vessels to work together for a larger goal, then you want to set up a Fleet. There is no way to explicitly create a new fleet. Instead, you have to chain multiple Vessels together for a Fleet to be created.
Create an initial Vessel that you want to be the first to run in your Fleet.
Within the same project, create a secondary Vessel that you want to run after your initial Vessel.
Under the Triggers section, select the "Internal Trigger" option.
Select the initially created Vessel.
Save the secondary Vessel.
Congratulations! At this point, a fleet containing the initial Vessel and the secondary Vessel will have been created. You can continue to add Vessels to the fleet by creating more and more Vessels that have Internal Triggers for Vessels in that fleet.
Learn what Fleets are and how they work.