[Tamlin]

I may be wrong but I believe the O.P. is asking about the actual technique of creating custom brushes and shapes. If that's the case:

CUSTOM BRUSH

1. Open the image in Photoshop.
2. If you only want part of the image to be your brush, select it with your favourite selection tool. A tip: if you're making a brush that will be used to apply a background texture, try feathering the selection so the edges of the brush will be easier to blend with others.
3. Select Edit > Define Brush Preset...
4. Give your brush a name and hit OK. Your custom brush will now be available in your currently-loaded brush set.

To save your new brush(es) to a new set, select Preset Manager from the Brush Tool's drop-down menu. Click on the brush you want to save (or use Ctrl+click to select more than one), then hit Save Set...
Give your new set a name.

CUSTOM SHAPE

Creating Custom Shapes is a little different: a custom shape is defined from a path, so if you want to create a custom shape from a bitmap (rather than a vector) you first need to define a path from your shape. The easiest way to do this is to select the area (again with your Selection tool of choice), then right-click the selection and choose Make Work Path... Set the tolerance and hit OK. You can now select Edit > Define Custom Shape...

Hope this helps.