First you should understand that the project have many others distinct codes, because we want to adapt the project to any kind of sensor or microcontroller, this will make it more accessible to everyone.
The first step is know what is the project you'd like to build based in the sensor and in the microcontroller.
For example, to build the project with the Arduino UNO/Nano with the HC-SR04 sensor you may choose the Helen_Single_HC-SR04 project version.
If you'd like to make the project from scratch (You'd like to search all the materials needed and build it), you may choose any version, because for each one has a list with all required components for the building. We recommend you build the Helen_Single_HC-SR04 version.
Just click on the project you'd like to build and you'll be redirected to the tutorial of it.
More versions will come soon