Go to 'Settings -> Integrations'. Select Salesforce from the list of integrations.
Click the "Connect to service' button. This will open Salesforce. Enter your credentials to login to Salesforce. Allow MakePlans to access your Salesforce account.
You will then return to MakePlans to select which MakePlans account to connect to. Select your account.
That's it. MakePlans will now automatically add a new contact Salesforce whenever a new booking is made.