There exist numerous possibilities to measure temperature. On is the Dallas DS1820 sensor. It uses a single GPIO. It is necessary to define that this GPIO is used for a 1-wire bus. And then, the 1-wire bus is referenced by its id in the sensor itself:

one_wire:
  - platform: gpio
    pin: GPIO12
    id: wire1

sensor:
  - platform: dallas_temp
    name: Temperatur
    update_interval: 5s
    one_wire_id: wire1

and it shows in HA: