Oral swab tests are pretty simple: They put the swab in the inside of your cheek for 3 minutes and then swab the inside of the mouth before taking it out. The swab is then tested. Oral swab tests are only good for detecting recent use.. Urine testing is much more accurate.
You open your mouth, they sick a swap in for a few moments and pull it out and see if the test strip changes color. Simple.