We present a careful and detailed light-curve analysis of publicly available I-band data on fundamental mode RR Lyrae (RRab) stars of the Large Magellanic Cloud (LMC) obtained by the Optical Gravitational Lensing Experiment phase-III project. Using the Fourier parameters of 13095 RRab stars, metallicities and absolute magnitudes of individual stars are obtained. The representation of stars on the P-{phi}_31_^V^ plane shows the existence of three significant metallicity groups with mean metallicities as -1.20+/-0.12, -1.57+/-0.10 and -1.89+/-0.09dex. The corresponding absolute magnitudes of these three groups are obtained as 0.70+/-0.08, 0.59+/-0.06 and 0.49+/-0.08mag, respectively. Distribution of these three groups as a function of vertical |z| distance indicates that the formation of the LMC disc predates the formation of the inner halo. Issue of the existence of a metallicity gradient as a function of galactocentric distances has also been addressed. Approximating the structure of the LMC disc as a triaxial ellipsoid, the inclination angle (i) relative to the plane of the sky and the position angle of the line of nodes ({theta}_lon_) were estimated as 24.20{deg} and 176.01{deg}, respectively. The axes ratios and the eccentricity were also determined using the principal axis transformation method.