To add FedEx as a carrier, you will need the following:
You receive these credentials from FedEx on an e-mail. In case you have lost them you can always contact FedEx and ask them to resend.
To add FedEx as a carrier, you will need to do the following:
Navigate to Webshipper and then go to Settings > Carriers > FedEx
Once you get there, you insert the credentials in the fields.
Once you have added them, you press "Create carrier"
Congratulations! You have now added FedEx as a carrier, and you should be able to use their services in the future!