By completing order you earn money and gain experience points (EXP). You gain 1 EXP for each kilometer with a cargo. Your skills allow for gaining bonuses apart from money and EXP. You may get some extra payment. Notice, that the bonus payment corresponds with your driver's level (second row). Below you can check other bonuses depending on the order type (e.g. dangerous substances, cargo of high value, etc.). When you gain enough EXP, your level will rise.
You can check in the table below how many EXP points you need to level up.
The main panel ([Escape]) available in the player's profile allows you to check the "progress history" where a diagram displays the number of EXP points gained for various orders, total number of kilometers and other statistic data.