Tampers are an important tool in the preparation of coffee, there are many styles of coffee tamps available for you to use when preparing espresso. The tamp you choose will depend mainly on your personal preferences and the type of coffee machine you will be using.
Hand held tamps are generally the most widely used style of tamp by baristas as it allows portability and a greater degree of control. A quality tamp will consist of a generally flat (occasionally convex) base - this is the part that comes in contact with the coffee, it will also have the handle which should be chosen to ensure it is a comfortable fit for your hand.
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Most hand tamps are simply a solid unit which you can use that often come with custom handles. It is also possible to purchase spring loaded tamps which assist in delivering the correct amount of pressure when tamping - especially good for improving consistency or possibly if you are new to brewing espresso.
So how do you properly hold a hand tamp? Well think of it as if you are gripping a bicycle handlebar, start by wrapping your hand around the handle so it sits neatly in the palm of your hand. Place your thumb on the top of the base as this will give support and control. You can find a complete rundown of correct tamping method on my How To Guide: Tamping.
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The other variety of tamp is that which is fixed to a grinder. It is common to see these in cafe's and coffee houses. These are a flat disk attached to the grinder in which you press the porta filter up against, the pro's to using a tamp like this is firstly that it can't be lost and is consistent in the sense that different baristas can use it and achieve much the same result without the need to vary the grind. Some of the drawbacks to this method are the lack of control and the fact that it is easier to create an unlevelled tamp.
At the end of the day it is personal preference as to which you chose to use, in my personal experience a well made and designed hand tamp is far more effective than the style fixed to the coffee grinder and is a great investment on that journey to creating some awesome espresso.