I made a 10 euro deposit but I cannot play neither casino nor slots. My cashier seems to be empty.

In order to be able to play with real money, you must buy casino chips from your account.
To transfer money from your account (Total Credits) to your casino account (casino) you have to click on blue bar above the menu and enter the number of chips you want to transfer. If you want to buy chips and play casino you have to enter the amount and click on buy. If you want to transfer money to your account you have to click on sell.