To connect the Arduino Nano (U1) to the GSM module (SIM800L), we need to establish serial communication between them. The GSM module communicates through its TXD and RXD pins which will be connected to corresponding RX and TX pins on the Arduino Nano. Since the Arduino Nano operates at 5V and the SIM800L typically operates at a lower voltage (around 3.3V to 4.2V for many GSM modules, please verify the SIM800L datasheet for exact voltage levels), it's important to ensure that the voltage levels are compatible or use level shifters if necessary. However, in many practical applications, direct connection works, but this depends heavily on the specific GSM module's tolerance.

Given the pinout you've provided, here are the connections to make:

Additionally, ensure both modules share a common ground:

For the GSM module's power, if your SIM800L module can operate safely at 5V (verify this with datasheet or module specs), you could directly connect:

If the SIM800L requires a lower voltage, you'll need to use a voltage regulator or a buck converter to step down the Arduino's 5V output to a suitable level for the GSM module. Assuming it operates at 3.7V (typical for Li-ion battery-operated devices, but again, please verify with your specific module's requirements), and without a specific voltage regulator for this in your list, this connection will depend on your method of voltage regulation.

These connections should establish basic communication between your Arduino Nano and the GSM module. Always verify the voltage compatibility and consider implementing voltage level shifting where necessary to avoid damaging your components.