To upload your compiled program to the ESP8266:
- Diconnect power to the ESP.
- Bring GPIO0 to ground (press AND HOLD DOWN the pushbutton).
- Power up the ESP.
- Release the pushbutton
- Click the round right arrow icon to upload the program
If you have errors in communications, check your connections and that you have the serial port selected appropriately. Hopefully the right color wires from the serial cable are connected to the ESP-01 module.
When it works, you should see the tiny blue light on the ESP-01 module flashing and the following display on the Arduino IDE:
Once the upload stops (second set of periods stops updating), your program is loaded and running. If it does not appear to run, you can unplug the power and replug in the power.
Open the Arduino IDE serial terminal by using the menu Tools -> Serial Monitor. Set the baud rate in the bottom left (red circle below) to 115,200 baud (default for current firmware, older firmware was 9,600 baud). You should see a screen like that below:
When the project powers up you'll get some random characters then some periods as the ESP8266 connects to the router where you specified the SSID and password in your Arduino sketch (you did change that, yes? If not, change the program and upload the new program).
When the ESP8266 connects to your router, It will say "DHT Weather Reading Server". Note the IP Address (in blue circle) for the next step.