New to ubiquiti eli5

Can someone eli5 the uses ubiquitis other products and why would i need them?

1. Uniquiti unifi cloud key
2. Unifi security gateway
3. Edge router

I already bought 3 unifi AP LR and 16 port poe switch. My house’s setup is just simple, maybe around 10 wireless devices (excluding the AP’s) and around 8 devices that are directly connected to the switch.