Short answers, pulled from the story.
A gauge boson is a bosonic elementary particle that acts as the force carrier for elementary fermions. Elementary particles whose interactions are described by a gauge theory interact with each other by the exchange of gauge bosons, usually as virtual particles.
The Standard Model recognizes photons, W and Z bosons, and gluons as the four kinds of gauge bosons. Photons carry the electromagnetic interaction while W and Z bosons carry the weak interaction and gluons carry the strong interaction.
According to the Standard Model, the W and Z bosons gain mass via the Higgs mechanism where electroweak gauge bosons couple to a Higgs field. This field undergoes spontaneous symmetry breaking due to the shape of its interaction potential resulting in a non-zero Higgs vacuum expectation value.
Isolated gluons do not occur because they are color-charged and subject to color confinement. Gluons interact with each other because they possess color charge themselves which creates binding energy that increases with distance preventing free gluons from existing outside hadrons.
The Georgi Glashow model predicts additional gauge bosons named X and Y bosons that mediate interactions between quarks and leptons. These hypothetical particles would be even more massive than W and Z bosons due to symmetry breaking but analysis has yielded no evidence of their existence.