chatcity

When Xion and I duel on Chatzy, this is how we do it:

We each keep a new tab open, or a new window open. (Preferably tab.)
If an opponent plays/summons/activates a card we don't know, we go to the new tab and search the name of the card.
Usually the first result of that search will be a YugiohWikia article that contains a picture of the card, and it's effect.
This process takes around 10 seconds to complete. Very efficient.