The vast majority of the weakly radioactive substances used in these tests are cleared from your body within a day or two. But even before then, you can interact normally with other people because there's no risk of exposing them to significant amounts of radiation from your body.
It takes an hour or more for the pictures to be developed and additional time for a radiologist to examine them. Your doctor will probably receive a report within a day or two.
The scan will show the outline, shape, and position of your thyroid so that the doctor can determine whether it is enlarged and whether there are any suspicious growths or nodules. The scan also provides a rough measure of thyroid activity, although this has to be confirmed with a radioactive iodine uptake test.