I'm trying to understand how everything works about pulse-dtmf-converter HOT 1 OPEN

Hi,
As shown in the readme, you can find more information on the Hackaday.io page.

1. see the pictures on the hackaday.io page
2. This project contains a Firmware folder. That's the firmware for the microcontroller on the board. If you take a look in the Hardware folder, you'll find a PDF of the schematic. It contains the microcontroller.

Your english is ok.

Please take some effort to go through the information that has been made publicly available to you (for free).
I have no clue what your skill level in electronics is or what is your motivation to make this project. This project might look easy, but it's not for beginners.

1. Soldering is not too difficult. Everyone who has ever soldered SMD should be able to do it with the proper tools.
2. You'll need to install VSCode, PlatformIO and build the firmware on your computer.
3. You'll need a programmer to upload the firmware from your computer to the microcontroller. I'm using the AVRISP MkII, but you can use something else.
4. You'll need an oscilloscope to debug when it doesn't work. Debugging can be very frustrating when you're not fully understanding what is going on in the circuit. This project is even harder, because the VOIP-box that tries to decode the DTMF-pulses will not tell you what's wrong. Either it works or it doesn't. The circuit might take a bit of tuning. It depends on your own installation.

from pulse-dtmf-converter.