Panning is the action of searching rivers for minerals using a Sift upgrade.
How To Pan
First, you'll need the Sift Upgrade on your Vacpac for 2000 Newbucks. Despite the expensive price, it'll pay for itself later when you find a lot of minerals to sell later.
Next, you press the / key to pick up a bunch of sand and items. But this won't be enough. You need to hold the key down for most efficiency.
Lastly, while still holding they key, you need to shake the sand out by moving around a little bit.
Every once in a while, something will wash up in a river or on the shores of a lake/pond. It usually is concealed by sand, although it may be partially visible.