What is a market order?
A market order is an order to buy or sell a stock at the market's current best available price. If a market order is placed when the market is closed, it will be executed at the opening price as soon as the market opens. Keep in mind that the last-traded price is not necessarily the price at which your market buy order will be executed and that there could be fluctuation between the executed price and the last seen price.
What is a conditional order?
A conditional order is a type of order where, unlike a market order, it will only be executed if certain criteria in the market is met. Examples include limit and stop orders.