Money is one of the fundamental concepts of the game. You spend them on buying stuff, paying taxes, infrastructure, employee/fixed costs, etc. You can earn them by selling things you produced, holding bonds, or by taking loans. However, you have to pay interests on those loans, making you lose money in the long term.
They aren't as crucial to gameplay as money, but are important nonetheless. You spend them to train staff, upgrade loan/overdraft limits and to upgrade storage. You earn them at rate of 2 points/minute, with additional 2 points if you're online. Donators get a flat bonus of 1 XP/minute, meaning they earn 3 (when offline) or 5 (online) XP/minute. If you spend 2 game coins, you earn additional 5 XP points per minute. The highest possible XP rate (online+donator+XP boost) is 10 XP per minute. Also, you can obtain up to 1 000 XP per day by voting.
Game coins 
Game coins can be used to buy a variety of additional options. A short list of these below.
- Experiance Boost
- Instant Shipping for the day
- No transport costs for the day
- Spy other players for 3 days
- Hide your profits for the FTA
- No overdraft interests for 2 days
- Double speed training for 8 hours on staff
- Avoid loan interests @ end of day