Example of an esphome configuration file - my bathroom sensor with temp, humidity, one switch and one relay (light) output.

bathroom.yaml

esphome:
  name: bathroom
  platform: ESP8266
  board: nodemcuv2

wifi:
  ssid: "ssid"
  password: "123"
  fast_connect: true
  
  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Bathroom Fallback Hotspot"
    password: "123"

captive_portal:

# Enable logging
logger:

# Enable Home Assistant API - This talks back to the datastorage and UI server
api:
  password: "123"

ota:
  password: "123"

sensor:
  # just sends the uptime seconds so we can see unexpected reboots
  - platform: uptime
    name: "Bathroom Uptime Sensor"
    update_interval: 300s
    
  - platform: dht
    pin: D4
    temperature:
      name: "Bathroom Temperature"
      icon: mdi:shower
      filters:
        - calibrate_polynomial:
            degree: 2
            datapoints:
              # Sensor is in a heated metal box, these values 
              # calibrate it closer to the air temp
              - 27 -> 23
              - 31 -> 24
              - 34 -> 27.2
              - 35 -> 28.3
              - 36 -> 28.9
              - 37 -> 29.4
          # sometimes the sensor reading fails and it sends "NaN" 
          # this blocks those messages
        - filter_out: nan
          # the sensor only outputs when it changes 
          # this resends the last value as a heartbeat signal
        - heartbeat: 15s
          # the sensor sometimes spikes or dips wildly during startup or from random events
          # this averages a few readings before outputing anything
        - sliding_window_moving_average:
            window_size: 2
            send_every: 2
            send_first_at: 1
          # the sensor reads in C, this sends F
        - lambda: return x * (9.0/5.0) + 32.0; 
      # this just sets the name of the units, we had to do the math above
      unit_of_measurement: "°F"
      
    humidity:
      name: "Bathroom Humidity"
      icon: mdi:shower
      filters:
        - calibrate_polynomial:
            degree: 1
            datapoints:
              # This humidity calibration is rougher, need more data
              - 16 -> 46
              - 15 -> 45
        - filter_out: nan
        - heartbeat: 15s
        - sliding_window_moving_average:
            window_size: 2
            send_every: 2
            send_first_at: 1
      accuracy_decimals: 1        # humidity gets 0 decimals by default
    model: DHT11
    
   # reports signal strength as a diagnostic value
  - platform: wifi_signal
    name: "Bathroom WiFi Signal Strength"
    update_interval: 300s

binary_sensor:
   # this pin connects to the old rocker switch on the wall
  - platform: gpio
    name: "Bathroom Switch #1"
    # PULLUP enables resistors on the microcontroller that help clear any
    # floating voltage to enable instant readings of switch change
    # floating voltage can keep the pin high for several minutes after
    # turning off the switch. I actually wired in my own resitors to get 
    # the same result, then discovered this one line fix. 
    # Inverted to match pin state to switch status
    # because that's the way it is
    pin:
        number: D5
        mode: INPUT_PULLUP
        inverted: true
    # delay shutoff because the switch makes and breaks multiple times as it turns off
    filters:
      - delayed_off: 60ms

# this tells the system there's an output (relay) connected to this pin
output:
  - platform: gpio
    id: bathroom_ceiling_gpio
    pin: GPIO5

# this tells the system that the output we made operates a light
light:
  - platform: binary
    id: bathroom_ceiling
    name: "Bathroom Ceiling"
    output: bathroom_ceiling_gpio

text_sensor:
  - platform: version
    name: "Bathroom ESPHome Version"