It's an order to buy/sell perps immediately at the next price available. Although you won't know the order's exact execute price but it's guaranteed to be filled ASAP.
One important thing to remember is that the last traded price is not necessarily the one your market order will get.
In fast-moving and volatile markets, prices change fast, the cost might have changed a bit from what was last posted on the screen. The price will remain the same only when the bid/ask price is exactly at the last traded price.
Limit orders can be created by selecting the "Limit" option after selecting whether you would like to open a long or short.
A limit order sets the maximum or minimum price at which you are willing to long or short.
After creating a limit order, it will appear in under the "Orders" tab, you can edit the order and change the trigger price if needed.
You can also put down limit order when you want to close a position.
Note that limit orders are not guaranteed to execute, this can occur in a few situations including but not exclusive to:
1. The mark price which is an aggregate of exchange prices did not reach the specified price
2. The mark price was reached but there may not be sufficient liquidity to execute the order
3. The mark price was reached but executing the order would result in a position which exceeds the current max leverage
4. The mark price was reached but the max allowed leverage would be exceeded
You can set stop-loss and take-profit orders by clicking on the "Close" button and selecting the "Trigger" tab.
After creating a trigger order, it will appear in your position's row as well as under the "Orders" tab, you can edit the order and change the trigger price if needed.
If you close a position manually, the associated trigger orders will remain open, you would need to cancel them manually if you do not want the order to be active when opening future positions.
Note that orders are not guaranteed to execute, this can occur in a few situations including but not exclusive to:
1. The mark price which is an aggregate of exchange prices did not reach the specified price
2. The specified price was reached but not long enough for it to be executed
3. The order's size exceeds the remaining position size
4. No keeper picked up the order for execution
Additionally, trigger orders are market orders and are not guaranteed to execute at the trigger price.