Once you set all the parameters of your order click on Create Order and confirm the transaction in your wallet.

If you trade with a particular bucket or open a specific type of position for the first time, or didn't provide big enough approval earlier, you need to Approve spending assets in your wallet. If you click the checkbox 'Allow using my balance for further transactions without approval', you will not have to send the approval transaction again.

NOTE: Don’t worry if you see the amount in red and the warning icon, it will show only if you put that checkmark and it’s just the maximum number available in the programming language that is pushed to MetaMask by Primex as the spending limit. Just click Next and then Approve.