Primarily just financial information. However some factions do sell stock as a way to get discounts or in. Some cases to buy back at a higher purchase rate. Stocks here don't nessasarily work like the real world stock market.
Unlikely that you will be able to scrounge enough stocks to own a faction just by buying from the market. Pretty much all owners keep at least 51% of the stock to prevent people from obtaining ownership from them. Unless they sell the faction, then they hand over the stocks to the new owner.