"An escrow service is a licensed and regulated company that collects, holds, and sends a buyer's money to a seller according to instructions agreed on by both the buyer and seller. Typically, once the buyer receives and approves the item from the seller within an agreed time frame, the escrow service then sends the payment to the seller."
Basically, how the service of escrow.com works, is this way.
You are the buyer. You buy an item online. You send the money to the escrow service. The seller sends the item to you. Once you recieve the money, the escrow service sends the seller the money.
You need to be cautious though and use only verified legitimate escrow services as there are scam escrows out there.
Cost seems to be $25 for anything less than $500. Rates can be calculated on Escrow.com