FieldInsight has two types of Customer records; 

Account and Site.  
NB:  Everyone uses these differently but there are slightly different workflows for each and this article talks about Adding an Account customer and being to quickly get in to the Booking Job workflow.

When you know this is a new Customer that you have to capture details about then this workflow has to start from the Job menu (NOT Customer menu)

Click to Add job

Click the + to Add a new Account customer

New Account customer details and Click 'Save account customer'

You are returned to the Job Booking page with the Account customer already associated.
Complete the Job Booking details and Save

Result:  A new Account customer is created as well as a New Job booked

Check out the video below