1st thing to do is to go to manage fleet and get of anything in there. next go to the market and try to sell enough minerals food etc to go into positive credits again. During this time dont use turns as the debt interest could be higher than you per turn income moving you further into debt. Check your important events until the items have been sold and then log out and log in. This should update your money. If you are in positive you can go back to using turns. If not and you have nothing left to sell you will have to try getting someone to use small positive artifacts to bring you close enough to $0 that your income is higher than the debt interest of restart.
As for making money, the chances are you are currently a terran and as a new player the best way for you to learn would be to research and build commercial on all colonies, this will give you a decent per turn income. You can buy any necessary food from the market(for a comm terran goods arent really needed)