I got a scholarship, which is more than what I need for the period of my studies. So, approximately 300 to 400 euro is in excess, what can I do with this money? I am 20.
what can I do with this money?
Save it and pay fur future periods. Assuming you can eat and live without it, the best thing you can do is save it until you get through school (avoiding loans as much as possible).
Investing it in relatively safe investments isn't going to change your life in a good way, but ultra-risky investments (leveraged FX trades, etc.) can go horribly wrong, causing you to lose it and more.
Once you're out of school, then you can start thinking about investing it.
Your answer should depend on how risk averse you are. If you are extremely risk averse, you should set aside the money in a savings account for an emergency fund. If you are less risk averse, then I would recommend investing all of it in a diversified mutual fund. Because you're only 20, your investment horizon should be pretty long, so you shouldn't have to worry about making extremely safe investments (bonds, CDs, and such).
Other options include: spending the money to travel or visit relatives (investing in personal relationships and your relationship with the physical world), using some of the money to buy books to learn how to invest that money (investing in knowledge), or even picking several stocks on your own and just investing with experience.