Everyone has the same genes with very few exceptions. What changes person to person is the allele which is the specific mutation of said common gene.

Here's an analogy. Say you own a blue Honda Civic and your neighbor owns a silver one? Do you have the same type of car?

Of course you do they are both Honda civics they only differ in their paint color. Alleles work the same way. Most variants are only 1-5 bases removed from any other version since greater mutation tends to break the gene outright instead of creating a variant.

Do an example of an actual allele i have blue eyes so I know both copies of the gene that controls it (this is oversimplified but I'm trying to be quick and easy) code to produce very little melanin in my iris.

Someone with brown eyes has the exact same gene controlling their eye color but it is just ever so slightly different and as a result tells the body to produce more melanin resulting in brown eyes.

The human genome project while representing only a few different alleles represents 99.999999999999% of the genes found in the entire human population. As a result you can base a lot of conclusions on it and with the advent of widespread DNA testing we are building libraries of different alleles which will allow for even more targeted medicine going forwards.