Shares are pieces of properties that each player can purchase.
At the beginning, every property has 1000 shares available.
You can buy them from the bank or directly from other players, if they already own them.
If there are no shares available and other players don't want to sell theirs - do not worry!
Once the number of shares available for purchase from all properties in the near area combined drops below certain amount, new shares will be added to all those properties.