In order to create Multiple Fleets, you should have already created your first one. This means that you are probably accustomed to the way the Fleet Management page works.
Now, click on the Vessels tab and try to add a new vessel to your fleet. This time instead of clicking on the Add to default fleet button, click on the down arrow at the right end of the button and then on the Add to new Fleet option that will be brought out.
You will then be asked to name your new fleet. Name it as you please and click on the Create Fleet button to complete the creation of your new fleet.
Moreover, you can create a new fleet from Data Exploration Tool as well. When you have finished a search, and you have found more that one vessel that you want to add to a new fleet, you have the option to select multiple vessels and create a new fleet with a click of a button!
Click on the adjacent button on the left side of each result to select it. The selected will appear green and a new button will appear on the button that reads Add to new Fleet. Type a name for your fleet, select a color and click Create.