An order is an investor's instruction to buy or sell securities. The orders entered by investors are collected in what is known as the "order book" and sorted by limit price and time of entry. As soon as compatible buy and sell orders are available, the trading system automatically executes the transaction by matching the respective orders.
Sample excerpt from the order book

How do you set the desired buy or sell price for your securities?
By specifying different order types, investors can ensure that they can buy or sell at a specific price.
Orders can be placed in the following ways, for example:
- Market Order
Market orders are unlimited buy/sell orders (“at-market orders”) without a specified price limit at which the order is to be executed. With this order type, the entire order is executed as quickly as possible at the best available price. - Limit Order
Limit orders are buy/sell orders with a specified price limit that are to be executed at the specified limit price or better.
For more detailed information on this topic, see order types.

