Some people play the market.
Others just spam fleet actions with escorts non stop.
You don't get energy credits for fleets though if you don't have the mission. I did it, then a bunch more fleet, and all I get are SP for each ship. Buddy hasn't given me the actual mission a second time.
how are people making so much money already, what the heck?
If your goal is to MAKE that much credits you can do it. The exchange is great for this if you can start out with a few items to sell. Buy low and sell high, rinse and repeat.
If there are 10,000 people playing and on average each person has 2000 or 3000 to spare that means that there is a basic economy for the exchange of 30 million credits and thats just today. That market grows every day. There are people that will sell things and make a profit and not play the game except to make more credits. I like to do that myself. Ive only got about 20k credits from doing that but I only play a few hours each night.