First, pretty much everything in the lite-hobby space is done with microcontrollers, Arduino being the most mature ecosystem. Arduino is a really fancy wrapper/

First, pretty much everything in the lite-hobby space is done with microcontrollers, Arduino being the most mature ecosystem. Arduino is a really fancy wrapper/standard around the AVR ATMegas, I would start here. Arduino is an Open Source project so many manufactures create an Arduino-compatible board, but i do recommend supporting them and buying your first Arduino UNO from them directly if you are able to. Arduino provides software and an easy way to interface with pinouts. Start by doing some of the sample projects and tutorials, you'll pickup some basic electrical theory along the way. Next, you will eventually ask the question of how to make a production board, where you may go down the rabbit hole of programming the AVR directly (the microcontroller), which I recommend as a jumping off point into raw microcontrollers and using an ICSP which an Arduino UNO can also do for you. Somewhere along this path, you will want to gather some more advanced knowledge of circuits and DC fundamentals. Pick up a set of 7400 logic chips and learn how logic gates work from the lowest level possible as well as op-amps, comparators, etc. You'll find every chip (IC or integrated circuit) speaks in either a protocol/bus or just logic levels (pins going high or low). When more than a bit or so of data is required to be transferred, ICs will implement a general-purpose digital interface like I2C (most common), SPI, or UART. There are some additional ones like I2S (for audio), 1wire (for one wire communication), CAN bus (what your car likely uses), and there are some more advanced ones like PCI (the same kind bus your PCI slots in your computer uses), MII (media independent interface), etc. Most of the time, you are just connecting together devices on a bus (for example I2C can support multiple devices because it's addressed) or finding ways to convert one to another (for example, you might want to communicate in RS232 via your UART bus). There is also analog which is a whole different beast. This is all a big simplification, but honestly it's not that unapproachable these days, just start small and build from there.