You can archive your finished jobs by selecting them in your list and clicking on Actions > Archive.
You can then access your archived jobs by clicking on 'View archived jobs' at the bottom of your list of jobs.
To unarchive a job, you have to go in the Archived view of your list of jobs by clicking on 'View archived jobs' , select the jobs you would like to unarchive and click on Actions > Unarchive. The jobs will then go back to your active view. You can also unarchive a job by clicking on Actions > Unarchive in the details of the job.
You can also archive and unarchive your clients, suppliers, quotes, invoices, expenses and purchase orders by using the same buttons: Actions > (Un)Archive in the list or in the details, and 'View archived items' at the bottom of the lists.