On the MoDOT website, hover over Doing Business with MoDOT and select Electronic Signatures.
That will take you to the general information (landing) page for Electronic Signatures
On the left hand side of the page under Explore, there is additional information about DocuSign and an online form to request a PIN code.
On the DocuSign page, there are step by step instructions with screenshots on how to sign an agreement with DocuSign. There is also a short video clip walking the signer through the process.