The UNO and the ESP are connected together via Serial… SoftwareSerial on the UNO and the hardware serial pins on the ESP8266.
If I recall, Pin 7 on the UNO is RX, so needs to connect to the TX pin on the ESP and the ESP RX pin to pin 8 TX on the UNO.
Something to note though, is that you should use a voltage level shifter module between them as the UNO sends out 5v on i’ts TX pin… but the ESP only wants to see 3.3v on it’s RX pin.