I am a newbie. I purchased about $2,500 worth of ETH 4 days ago. I want to use it now. Is that possible or must I wait until it is in my wallet? I could have made a quick profit if I was able to sell it!
In general, you are able to spend your Ethers once the purchase transaction is confirmed (you can see the ETH in your wallet). 4 days is more than enough for a transaction to be confirmed, I think you have already your EThers, if you have your address you can check your balance using https://etherscan.io.
Based on your question I'm going to guess that you purchased on Coinbase.com or a similar website. So here's the thing, ethereum transactions don't usually take that long if you are just sending peer to peer. No, you can't send your ETH before they are confirmed. Now coinbase or other websites have their own policy since they're taking your checking account they have their own policy to ensure payment is cleared. Generally speaking it's better to buy peer to peer.