There are currently two kinds of bonuses:
The market bonus gives you one iKr extra in Net Worth Company Value.
The amount of market bonus you can have is determined by the amount of goods you produced yesterday less any goods you subsequently used in your higher level factories and shops and finally less any units sold to the bank.
So for example you produced 5000 units of wheat, used 1000 units of wheat in your brewary and sold 1000 units to the bank. This means your maximum market bonus available the following day is 3000.
To get the bonus you need to sell 3000 units on the market. and remember you need to sell the goods the day after they are produced (not literally the bonus is just made available from previous days numbers)
Purchase Bonus The other kind of bonus is money you get from units you have bought on the market. If you later use those units in your factories, you will get back a percentage of what you paid for the units. This sort of bonus can give you max 2500 iKr per round.
You can see how much bonus you currently have available by clicking on the Bonus-link.