wow...this thread makes me sad....so many players don't bother to read their manuals in games anymore.
Pro Tip: Take your manual with you to the Bathroom, it makes excellent potty time reading.
Little excerpt for you:
FLEET LOGISTICS
There‘s a limit to how many ships an empire can field at the same time, which is represented by your fleet supply. Each faction begins with 100 fleet supply points, which is the base amount any race can manage without additional research. Every ship drains some of your available points, with frigates requiring the least and capital ships the most.
Once you‘ve maxed out your available fleet points, you won‘t be able to field any additional vessels. The amount of currently available fleet points is displayed at the top of the gameplay screen. By mousing over this number, an InfoCard will appear that will list your total points in use and how your points are distributed across your ships.
In addition to fleet supply, capital ships require special commanders before they can be constructed. Each player starts the game with the ability to field one capital ship, which should be used wisely. In order to construct additional capital ships, players must research advanced training technologies. The number of available capital ship crews is displayed next to your fleet supply at the top of the main gameplay screen. By mousing over this figure, you can see where your commanders are deployed.
There I underlined it for you. If you bought the game digitally then you can always just print out the pdf manual, which I copy and pasted for your viewing pleasures.