Market orders are likely the first order you’ll encounter when investing and are dollar based.
This means they’ll be executed at the best available price based on the amount you’ve decided to spend.
They’ll also be executed quicker but are also more subject to the liquidity of the market. As a result, the actual amount of stock you receive may be more, less or fractionalised.
As with any order, they can be placed at any time but executed only when the market is open.
While the market is open, your orders will be executed at the best available price.
If you’re buying, this will be the ask price, if you’re selling, this will be the bid price.
Lastly, it's important to note that the execution of all market orders are subject to availability and not guaranteed to be completed within a particular trading session. These orders will remain queued until they are executed or deleted by you.
For more information on why an order may not be executed What happens if a share spikes in price?