Not the place for a quiet cappuchino and a biscuit. Coffeeshop is the euphemism for a place where you can buy hashish and cannabis over the counter. Amsterdam has hundreds, but the regulations have been tightened up in recent years. And any whisper of hard drugs under the counter and the place will be boarded up.
Coffeeshop etiquette? Haven't got a clue these days. You can spot them by the green and white sign discreetly displayed on the door or window - this is the official Amsterdam city council licence. Most city centre coffeeshops are full of tourists - the liberal attitude to drugs is a major tourist draw, even if the tourist board likes to pretend everyone comes here for art.
I'll leave this to the website of an expert. It also has information about smart shops and head shops. Love the jargon.