What exactly is a boson?
A boson is a particle whose spin (= intrinsic angular momentum) is an integer number. For example, the photon (the particle that is responsible for the electromagnetic force) is a boson. Contrast this with a fermion, such as the electron, whose spin is a half integer. In everyday terms, the bosons are the microscopic particles that make up the forces: electromagnetism and gravity, as well as the weak and strong forces. Fermions are the particles that make up matter: protons, neutrons, and electrons. The fact that forces come from bosons while matter comes from fermions is a very deep observation, and is related (at least in part) to something called the 'spin-statistics' theorem, but let me not go into that.
Now let me note that all the bosons that are responsible for producing forces have spin 1 or 2. The Higgs boson is another kind of boson, which does not behave like a force. Technically, this is because its spin is 0. In fact, it is the only fundamental particle with spin 0 that we know exists: all the others that are known have spin 1/2 (fermions), 1, or 2.
Is the Higgs boson the cause of gravity or a result of it? Does the collision of particles at the LHC create a gravity field or waves or somehow interact with the gravity field of the earth?
The Higgs boson has nothing to do with gravity. It does not cause gravity and it is not the result of gravity. The particle that 'causes' gravity is called the graviton, it is a boson like all the other force-particles, and it has spin 2.
The Higgs boson does give mass some to the other fundamental particles, and this mass then interacts with gravity just like all other mass. But this is an indirect relation.
The particles at the LHC interact with the gravitational field of the earth just like all other particles. As part of the collisions, certainly some gravitons (= 'gravity particles') are also created. But these are completely negligible effects that can be ignored, because gravity is a much weaker force than all the others.
The Higgs Boson is supposed to be quite massive and equivalent to a large number of protons. Were many particles needed to create it or only a few travelling at high speeds? Was the high energy converted into the large mass?
I am not sure what you mean by 'equivalent to a large number of protons'. It is true that if you weigh one Higgs particle it will weigh as much as about 120 protons, but they are not related beyond this simple fact.
The Higgs particle, like all other particles produced at the LHC, is created by a collision between two highly energetic (= very fast) protons. Indeed, in the collisions in which a Higgs was created, the energy of the protons was converted into the mass of the Higgs particle.
Why is the particle so short lived and what does it decay into?
The Higgs is short-lived essentially because it is very massive. Roughly speaking, the more massive a particle is, the faster it decays into other particles. This is not a precise statement because it really depends on what the particle can decay to. For example, the proton is massive relative to the electron, but it seems not to decay to anything due to various reasons.
The Higgs particle has different possibilities to decay to (these possibilities are called 'decay channels'). For example, it can decay to two photons, or to two quarks like bottom and anti-bottom.