In Trading an order is a set of instructions to a broker to buy or sell an asset on a trader’s behalf. An order can be used to buy and sell securities like stocks, currencies, futures, commodities, options, bonds and other securities.

Exchanges trade securities through a bid/ask process i.e buyer will be matched with the seller and vice-versa.
There are multiple order types which will affect price the investor buys or sells a security at,  when they will buy or sell and also whether the order will be filled or not.

Trader will  choose the order type depending on the trader’s strategy  for the security , whether they want to get in and out quickly, and/or how concerned they are about the price they get.

Here are some of the most important order types :

• Market Order : This type of order from Trader instructs the brokerage to complete the order at the next available price. 
• Limit Order   : Limit Order from Trader   instructs the brokerage to buy a security at or below a specified price. Here are some sub-types of Limit Order :  Buy Limit, Sell Limit, Buy Stop, Sell Stop
• Stop Order : This order type from Trader remains dormant until a certain price is passed after which the order is executed as a market order. 
• 

• Conditional Order :This type of order from a trader  will only execute if certain specified conditions are met. This will allow  cautious  traders or investors to engage in trades without having to be present   in front of the screen.  Trader has to  first specify a price condition then specify an action if that condition triggers.
•