Job approval is an important feature for project managers or account managers. It allows you to review all the time and activities logged against a job, make any important adjustments and then "approve" a portion of work for invoicing.

From the View Job screen, select Process > Approve
Alternatively, you can click the Approve button next to the Budget & Work section.
From this budget section you can actually confirm how much time has already been approved for this job. The advantage of approving time is you can produce an invoice with an amount specific to the approved time. - this is great for progress invoicing.
Once approved time has been invoiced then it will no longer show in the Approved time section but it will show under the Invoices tab.
The Approving Job screen will load:

This screen provides several features for tidying up the work logged against this job:
Note that the monetary amounts ($) may change if you move an activity from a component with a specified rate to one that is set to use Staff rates.
You can now either "Save" and any time changes or relocations will be saved, but the activities will remain unapproved. Otherwise, "Save and Approve" to commit these changes and "lock" those activities ready for invoicing. You cannot approve these activities a second time. Note that any activities/components that are deferred will be visible the next time you approve the job.
If you work with a client on a retainer basis, they may ask that you allocate time from a job against one of their retainer periods (ie, a contract package). In which case, when you approve a job, the Approving Job screen will list any available contracts and their packages by date - visible in the drop-down list near the top left corner. You can also see the allocation vs budget for each package:

You can only select one package for each approval. Note that if you only Save, then all changes will be saved BUT the activities will not be packaged/approved.

If you allocate time into a package then you would normally invoice for the contract package - not the job.