As of now, Raspberry Pi has the smart weather station sensors attached to it. Now, we are going to add a relay to the setup.
A relay is an electrical switch that is driven by an electronic signal. That is, triggering the relay with logic high 1 will turn on the relay and logic low 0 will turn off the relay.
Some relays work the other way around, depending on the component. To know more about types of relay and how they work, refer to, https://www.phidgets.com/docs/Mechanical_Relay_Primer.
You can purchase a simple 5V driven relay from Amazon: (https://www.amazon.com/DAOKI%C2%AE-Arduino-Indicator-Channel-Official/dp/B00XT0OSUQ/ref=sr_1_3).