If you remeber potato stamps from childhood you can imagine how padprinting works. The most important tool is a stamp called pad. It transfers the paint from matrix onto the printed product. The matrix is engraved with laser to create cavity corresponding to the design. Each color requires separate matrix and pad.
The main advantage of padprinting is print speed, versatility and accuracy. The only limitation of it is that prints can nor be made around round objects. Small curves are not a problem because the pad is fleqsible, but round objecs can be printed on its most flat surface, otherwise the imprint may be mishapen.
Technique designed specialy for round objects is screenprinting 360 degrees which allows to print around the product - for example, pen, mug or thermos. It's a completely different printing method which has not much to do with pad printing.
Most common padprinting machines allow to print up to four colors, and works great witb pens, keychains, mugs, lighters and other products. Basically the usage of it is limitless.