So I have started actually using bitcoins recently, have been a saver/hodler for 2 years.
The take-away express in the Netherlands lets you order food in bitcoin with zero fees (can save you some 10%).
So last time I noticed that my bitcoin mobile wallet (bitwallet) was empty so I bought some 20 euros of bitcoins online.
After the buy, my wallet had me wait for 3 confirmations (ca 30 min) before I could send out 10 euro worth of bitcoins.
I know that the takeway takes 0-conform transactions, or at least I get a sms-confirm directly, so I pressume as much.

So why is my wallet waiting for 3 comfirms on a small amount? Also are there any guidelines wallet-software could/should follow for confirms?
How does this work at the btc protocol? At which point can an output be used as an input ? After how many confirmations of the output ?