New users will need to enter MWS credential's at sign in.
Current users will enter MWS credential's after installing the latest build by going to File->Preferences->Amazon information and clicking on the green question mark button in the MWS Credential's section.
This will open a page in your browser that will direct you Amazon MWS.
You can also point your browser directly to- https://developer.amazonservices.com to sign up.
UK users need to sign up at https://developer.amazonservices.co.uk and DE users https://developer.amazonservices.de
On the next page, select the radio button that says “I want to access my own Amazon seller account with MWS”.
Click on “Next” and read the “Amazon MWS License Agreement”.
Click the box to confirm that you have read the License agreement and agree to the terms.
Then, click on “Next”