Optical solitons are wavepackets that can sustain the shape via a nonlinear refractive index potential well. They exist in a wide range of optical systems spanning optical fibers, fiber lasers and parametric oscillators. Recently, a new type optical solitons have been observed in coherently pumped high-Q microcavities. The observation of microcavity optical solitons provides a well-controlled experimental platform to study soliton physics. Microcavity optical solitons also endow an array of highly stable spectral lines in the frequency domain, which advance the miniaturization of frequency comb systems. These soliton microcombs have been self-reference stabilized and could enable many chip-based applications including optical frequency synthesizers, optical atomic clocks, data transmission, spectrometer and LiDAR in the near future. Here, the fundamental of microcavity optical solitons was introduced, with a special focus on soliton interaction dynamics. The microcavity dual-comb measurement based applications in fast imaging and mid-infrared gas spectroscopy were also discussed.