DocuSign is an optional way to sign. It is early access, so it appears only if your workspace has it. Connect it in Settings, Integrations, then use Send for Signature on a document.
Send
Choose the document (a contract, a change order, a lien waiver or a certificate) and then a signing method: Send via Email, or Sign In Person on the device. Enter the customer's name and email. If the contractor signs too, choose Both parties sign, or Contractor signs first, then customer. The app creates the envelope, makes the PDF and sends it. You are notified when it is complete. A contract signed on the device completes at once and the job is created.
Disconnect
Disconnect stops sending new documents through DocuSign and forgets which account it was, so the next connect can use another. Documents already sent stay with the old account.
Without DocuSign, proposals are signed in the app's own signing flow. See Getting it signed.