Info on how to set your files up with bleed and when and why you need a bleed.
The Edges of your print are important. Slight variances in the processes mean the paper might not be cut exactly on the cutline.
On a small piece like a business card there should be no text or graphics within 1/8 in of the edge of the final size of your piece. This is the margin type safety. (border)
Larger pieces will require a larger border.
If your piece has background image or colour extended it 1/8 in past the cut line. This is the bleed.
Here is also a link to Wikipedia with a further explanation.
This is an example for a standard 2 x 3.5 in business card.
Green line is the cut line and is the final size of the product.