When I search the message center I never get a result so I decided to post this here.
I looked through the rules and couldn't find any detailed information about stocks. I see players are selling them. How do they work? If I buy them is the only way I can make credits with them to sell them to someone else?
Yes, that is the only way that you can make money with most stocks. A few factions do have special arrangements where, if you own more than a certain quantity of their stocks, they may pay you a monthly dividend, but you would need to find out about that IC when you are looking around to buy stocks.
Otherwise, by default you do not earn any money purely as a result of owning a stock; its only consistent use is to allow you to keep track of some basic information about a faction such as its owner, value, other stockholders, bankruptcy status, etc. It is a fairly common practice for interested players to just hold on to one of each stock they can acquire to be able to pull up a faction's info if they want to.