Thanks for ordering an Yubikey with your SSL.com Extended Code Signing Certificate,
From the orders page when signed in at ssl.com, you should see your company name towards the center.
Click download right below that to go to the details.

Center column you should have an activate option where you will input the serial number printed on the Yubikey token itself.

After activating you will get your PIN that is used during the signing process.
You may also need to install the Yubikey mini-driver in order for the computer to pick up on the cert
https://www.yubico.com/support/download/smart-card-drivers-tools/

The cert should be visible in certmgr.msc in the personal certificates store
When using Signtool from the WindowsSDK, you will want to run a command similar to:
.\signtool.exe sign /fd sha256 /tr http://ts.ssl.com /td sha256 /n “COMPANY NAME” “C:\path\to\MyExecutable.exe”