There are two ways that you can create a new job.
The first way is from the jobs page, which you can get to by clicking Jobs on the top menu. Once there, you'll find the Create a New Job button on the top right. Clicking the button will take you to the new jobs page where you can enter in the services that the job will provide and either create a new customer for the job or select an existing one. You can also add any notes about the job that you might want to keep track of. After you've added the services and selected or created a customer, click the Create the Job button and your new job will be created.
The second way to create a job is directly from an existing customer. From the Customers list, click the customer that you want to create a new job for. Once on the customer's page, click on Choose an action and from that drop down menu select Start a new job. That will take you to the new job page where you can enter in the services that the job will provide and add any notes you want to keep for that job. After adding the services and/or notes, click the Create this Job button and your new job will be created.