Magnons are the quanta of spin waves, which exhibit the advantages of heat-dissipation-free and low-damping transfer of spin information over micrometeror even millimeter long distances in magnetic insulators, so that Joule heating due to charge flow can be avoided. This can overcome the increasingly significant issue of heat dissipation in electronic devices, so magnon-based devices have great potential in low-power, high-efficiency information storage and computing applications. In this review we first introduce the concepts of spin waves and magnons, and the advantages of magnons for research, then review recent studies of magnon transport in ferromagnetic and antiferromagnetic insulators, as well as new designs of magnonic devices. Finally, we present in detail our recent work on magnon torque induced magnetization switching at room temperature. This work is of significance for the development of magnonics and low-power, high-speed magnonic devices.