Connection to Salesforce is very simple. Just go to the Settings>Connectors and click the Salesforce logo.
Then, login with an admin account. Accept the authorization asked and you will be back on Signitic.
If your Salesforce account is live you should have blue icons in My users.
When the icon is blue it means the user is available on Salesforce and his signature will update on it. You can click on it to disable only the Salesforce connexion for this user.
You can update your signatures on the Dashboard or wait a day to see it updated.