I suggest going through depthai API docs; mainly, the neural network node and it's yolo and mobilenet versions (you can find them here under nodes. Check the input and output and make sure you fully understand what the network expects you to do. I personally wouldn't first start with standard NeuralNetwork node as it can get confusing with FP layers and result parsing.
We have many examples that pertain to the NN (find them under examples). Something like the yolo example would be a good starting ground.
Of course make sure to understand the framework of the model you are using. These are available all over the internet or you can watch some lessons on YouTube as well.
Let me know if you have any more questions.