If we can detect gravitational waves (if it exists) is it going to explain why the force of gravity is so much weaker compared to other fundamental forces or is it able to tell us why stuffs with mass attracts each other? Or maybe it will finally put some theories to rest?
None of the questions you put would be answered by the direct detection of gravitational waves, but there are many reasons their direct detection would be important:
1 As a Direct Confirmation of GTR
Gravitational waves are one of the last phenomena foretold by the General Theory of Relativity that have not been directly observed and compared with theory. Their finding would yield confirmation of GTR. On the other hand, failure to observe them at roughly the sensitivities expected of LIGO or the Einstein telescope in the next ten years would begin to falsify some of general relativity: we would have to come up with an explanation of why we don't see them when events that cosmologists believe are real (collisions between high energy objects) should, by GTR, bathe us in gravitational waves.
It should be noted, however, that we do have some fairly strong indirect evidence of gravitational waves through the observed spin down of the Hulse Taylor binary star system: the observed decrease in this system's orbital period since 1974 is almost exactly accounted for by energy loss owing to the gravitational radiation that GTR foretells would be output by this system.
2 Gravitational Radio Astronomy
One of the many reasons the possibility of observing gravitational waves is exciting is that they may be useful for gravitational radiation astronomy.
The earliest data on the early universe that we so far have are encoded in the cosmic background microwave radiation. We can "only" see back with this radiation as far until an estimated 378 000 years (i.e. about a third of a million years) after the big bang. This is because before that time, the so called recombination epoch, the Universe was opaque to light since it was a hot plasma of protons and electrons. Plasmas are not opaque to gravitational waves, however, so we could use gravitational waves from the early Universe to gather data about its structure before the recombination epoch.
Gravity is inertia and vice-versa. (equivalency principle) All matter deforms space-time, that's what gravity is. The spooky action-at-a-distance is objectionable to most theorists. So we have "Gravity Waves" from some, and the "Higgs Boson" from others, to explain how the deformation happens, but the truth of the matter is that no one knows what is being deformed in the first place! They simply define the deformation as how much gravity there is, how much light gets deflected, etc. Without ever saying what space-time is.