In standard escrow the market holds the money during the purchase. They are typically the most common types of market you will find. You send your coins to the market controlled wallet. If you received your order you tell the market to finalize your order and give the vendor your money.
Be careful: the orders finalize after some time automatically, in case you forgot to do it manually and so that the vendor has not to wait ages for his money.
If you have not received your order or have issues with it (it was less than the amount you bought or the product was not as advertised), you can dispute it. That prevents the order from auto-finalizing and you can resolve that matter along with a market staff member and the vendor in a discussion. The market staff member then decides after the discussion what actions to take (e.g. who gets the money from the order or if one of your violated the market rules). Remember to message the vendor first if you have problems with your order, instead of disputing it right away.
The big risk is that the market can always run away with that money. It happened a lot in the past, some examples are sheep market, Empire, evolution, abraxas, nucleus, middle earth marketplace.
So using standard escrow is discouraged and you should use alternative payment methods.