What does all of this mean?
Males are born with XY chromosomes. Someone who is male inherited his father's Y chromosome. Y DNA tests specifically look at the Y chromosome and compares them to other Y chromosomes. Those that match have a common male ancestor.
To illustrate, suppose John Doe had two sons. Jack Doe and James Doe. One male is a descendant of Jack. Another is a descendent of James. If the direct ancestor line is all men for both descendants, then they have the same Y chromosome as John Doe.
On another page I saw where John Lewis is my earliest ancestor. Is this so? What about all the other people on the cousin list, are they my cousins?
Depends on how you researched this information. If you went on Ancestry/FamilySearch and accepted every hint that came your way without question, then you didn't actually do any research. There is a possibility of error that increases significantly with each generation if you just accept whatever Ancestry tells you.
If however you started with direct family knowledge you know to be true and carefully made sure all the information was accurate before proceeding to the next generation, then the chances of errors are still present but much lower.