Ask HN: How to take readings from circuit boards with code?

I interviewed for a job at a robotics company that needs a software engineer. They are small but doing some amazing things. Its really exciting. They make their own boards and parts, etc.

They want software to control the robot, read signals it sends, send signals to it. The user interface will allow normal people to control it with no technical background.

I was honest and said even through I am very good at c++ I don't have any experience in this work. I have built Pi and a small Arduino based project. They still are expressing interest in having me work for them saying I can learn.

Can anyone give me pointers on how to get started learning about reading from boards, sending values, etc? I'd like to start learning now.