Everyone's eyes differ, but a figure of around 6000 visible stars is
often quoted (with around half visible from any point on earth). At
sea level in a rural area you might see around 2000, and in an urban
area you might be lucky to see 20.
You can't count the stars directly. Due to the rotation of the earth,
more keep appearing on one side and disappearing from the other. As
atmospheric conditions change, some stars become visible and some
become invisible. Instead, people look through a tube, count the stars
in that field of view, and scale that figure up to obtain an estimate
for the total.
If you want a specific number, The Yale Bright Star Catalog catalogs
the "naked eye visible stars", which they consider to be those with a
magnitude of 6.5 or brighter. Those have been catalogued and listed,
and there are 9110 entries in that list:
The Bright Star Catalog
But if you want to see all of them, you'll need ideal conditions: good
eyes, several high altitude viewpoints in different parts of the
earth, a moonless night, no aurora, and air that is absolutely still,
clear and dry.
Classification of star brightness as its "Magnitude" is explained here:
I trust this provides the information that you are seeking.
Google Search Strategy:
"there are * visible stars"
"how many stars"