You need to put in the amount of Bitcoin you want to get for your 60 EUR.
This will be based on the market price of the exchange.

Example: Current market price is EUR 450 for 1 BTC. Then 60 EUR will buy you 0.1333 BTC.
So you would put 0.1333 BTC / 60 EUR if you are willing to buy at EUR 450. You can put any price you want, if it is higher or equal than the current market price, the trade will be executed.