There are hundreds of different holsters- different materials, concealed, external, right or left handed, shoulder holsters, ankle holsters, holsters built into Bras, right side up, upside down, holsters for handguns, rifles and shotguns.
That is a matter of opinion. Many instructors (people that actually do it for a living) will tell you that the best way is in a strong-side hip holster, but many people aren't willing to carry a gun that way. The most basic answer is, there are many ways to carry a firearm. The best way for any particular person is whatever way that suits that person's lifestyle.
Many holster makers have one or more types that will fit.
Not exclusively. Police carry many different types, styles and finishes of firearm.
You need a license to carry a firearm in many places. You cannot carry one on an airplane.
In the US, hundreds of thousands.
It depends on what you mean. If you mean legally, it depends on the state. Some states require a handgun to be carried in a holster, but most don't. In Tennessee where I live, if you have a handgun permit, you can carry the gun any way you choose. Otherwise, you basic options are, holster or not in a holster.
There are many more than six.
A concealed carry holster can be ordered from several companies on the internet. The holsters can be bought in many styles and at many price ranges. Several websites offer free shipping, as well as, a comfort guarantee.
Leather holsters are used for many weapons, for everything from rifles to handguns. A small, inexpensive leather holster (usually a clam shell holster) for a handgun can cost less than $20.
Different Blackberry phones require different holsters; it is unlikely that a local store has holsters for all varieties in stock. Unless a local cell carrier store has the holster for your model, you would most likely be better served by ordering one from one of the many Internet retailers who carry them.
I'm going to guess that you're referring to an inside the waistband holster and an outside the waistband holster. An inside the waistband holster literally fits inside the waistband of your pants, and a outside the waistband holster fits on the outside of the pants, either using a belt or a paddle. The IWB is normally more concealable because it holds the gun much closer to your body, however, many people consider the IWB to be less comfortable.
Was it made for the Colt? Is it someone's old flap holster for a Colt 1917, and your Colt wound up inside? What's the condition of the holster? Too many questions to be answered.