What is Helium?
Helium is a cryptocurrency project. The Helium Network is a network of hotspots that operate is the 860-915 Mhz range that rewards "miners" for proving that they are providing network coverage. It does this by randomly selecting hotspots to challenge other hotspots by getting them to send out a RF signal called a beacon. When other nearby (or not so nearby) hotspots sense this beacon they relay this to the network and then they are selected as a witness to the beacon which rewards them as well. Most rewards will come through witnessing other hotspots, since the system is designed to only send out ~1-3 beacons per day on average, but this will vary because it is random.
What is Helium used for?
You can use the network for IoT devices such as mouse traps, soil sensors, GPS trackers etc. Helium is also building out a 5G network as well.