You can earn money and finance your company if your main business (railroading and city assets) isn't providing enough profit. All share rates are within a certain frame. Watch them a while to know where the low and highs are. The rates are cycling so what is down will go up some time again. Just be patient.
Calculation of profit:
Sales price (price per share at the time of closing the deal x number of shares)
./. sales fee
./. buy price (price per share at the time seting the buy order x number of shares)
./. buy fee
The fee is 10% from sales/buy price which is number of shares x price per share.
The daily variation is the difference to the last day's closing price (basically the midnight price) and is re-calculated every hour.
While the buy price rate is the one that is listed when giving the buy order, the sales price is determined at the time when the shares to be sold have found a buyer. So between giving the sell order and the closing of the deal the price might vary in both directions. the more shares you sell at once the longer it takes to find a buyer. To cancel a sales order is a valid option when the price for the shares dropped too much.
Dividends of shares held are taken at June 1st each year. (note to self: verify the date)
All 4 figures -- money you gain from selling shares, money you spent for buying shares, fees you paid for buying/selling shares and dividends you've got from shares held - are listed in the Balance sheet.