1. Open a new image by going to File> New. Any size will do, as long as it's not tiny. The background contents should be the default, white. Click OK. Set your colors to the default (black in the foreground, white in the background) by typing D on your keyboard. Then choose the Type tool from the toolbar or get it by typing T on your keyboard. Click on your image to start typing (this will automatically put your text on a new layer).
2. To make the © using a PC, hold down the Alt key and type 0169. On a Mac, press Option + G. Then type in a copyright notice (your name, your company, etc.) as you want it to appear. Pick a font you like -- you'll be stuck with it.
3. Now hide the Background layer. Do this by clicking the eye icon to the left of the Background layer's name on the Layers Palette. Make sure your Type layer is still selected (click on it if not). Then select your text: Go to Select > Color Range, move the Fuzziness slider all the way to 200, and click OK.
4. Then make your custom brush: Choose Edit > Define Brush Preset. Enter a descriptive name for the brush (like MyCopyright), and click OK.
5. To test your new brush, open an image you'd like to stamp. Grab the Brush tool (type B). Then, from the Options bar at the top of your screen, pull down the Brush menu and scroll to the bottom. The one you just made is the last on your list. Click on it to select it, then click the spot in your image where you want to stamp your copyright. If it's too small to see, increase your brush size.