A Path payment operation is a bit different types of Stellar operation because it needs to be done in a couple of steps.
Enter the destination account.
Enter the source asset.
Enter the source amount.
Click on "Next".
This will search for available payment paths that can fulfill your operation. If found, you can continue with step 2.
If step 1 is successful, you will be given a list of payment paths to choose from, similar to the image above. The list will contain the amount to be received by the destination account.
If steps 1 & 2 are complete, you can now specify the destination.
Enter the public key of the source account.
If you want the operation to be sent later, click on "Save", to add it to the operations queue and you are done.
To submit the operation to the network now, continue with the steps below
Click on "Send"
Submit the transaction