You first have to select all the jobs for the client. You can do that by using the filter in the list of jobs...

...Or you can click on the Jobs tab in every client.

Whatever the option you choose, you select the jobs to be invoiced and you click on the arrow > Invoice selected jobs. You'll arrive in the invoice containing all the jobs you selected, where you can edit the details of the invoice, generate the PDF document (by clicking on Actions > Generate PDF), etc.

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