Sure. Think of it like Lego bricks or one of those 1000-in-1 electronics kits. These kits don't do anything specific, they're building blocks you use to address a need you have in your home automation vision.

The ESP32 kits are just an ESP32 development board (mine are WROOM boards from Freenove) which has the microprocessor, headers breaking out the IO pins, and a "loader" module that facilities uploading code and is used to power the device with a USB cable. The boards also have onboard WiFi and Bluetooth radios. The -CAM variety has a low profile header to seat a small camera module (included). Look for "Freenove ESP32 WROOM" on your preferred online marketplace.

There are several ways to interact with (program) your ESP32 boards. The easiest and most straightforward is to use the ESPHome add-on in HA from the HACS store, along with the companion integration. The ESPHome add-on provides a software ecosystem of drivers and functions for a laundry list of hardware devices you can use in your project-- sensors, switches, lights, speakers, etc. The ESPHome wiki is sort of a catalog of supported peripherals you can easily use in your build projects. Many times, you can substitute components or extend an existing component driver. Mostly you assemble your components and the controller, and then write some YAML do tell ESPHome what devices are plugged into what pins. ESPHome more or less handles the rest.

The ESP32 integration creates HA devices and entities of the devices and sensors in the ESPHome add-on for use as triggers, conditions or actions in automation.

As for my specific doodads:

PIR is a Passive Infrared Receiver. It monitors its field of view for a change in infrared light (heat) which indicates a "hot.blob" has entered or left its field of view. The model I use, AM312, is designed to signal a change in IR light by raising a signal pin to +3 volts, which has applications in presence detection. It is fast, but not accurate. It also tends to "go blind" when the hot blob stops moving, and can be subject to false positives when the HVAC kicks on or by dappled sunlight

The mmWave radar is a Seeed R60A 60Ghz radar module. This particular module is optimized for human presence detection and fall detection. It uses millimeter wave radar to acquire and track humans in its field of view. 60GHz gives enough resolution to detect heartbeat, respiration and micromkvements like fidgeting. It talks to the ESP32 over the I2C bus (a digital IO bus similar to USB). It has advantages over the PIR sensor because it actively tracks its targets and can even tell if there are multiple people. Its less prone to false positives from environmental changes and smaller animals. Unfortunately, it can take several seconds to acquire a target and begin tracking it. In a presence application, a human could walk across several steps into the field of view within that time, giving the impression of a slow response.

Using both sensors in a presence application is a sort of belt-and-suspenders approach. You can compare the state of both sensors in your automations to determine presence with greater accuracy.

As for learning HA itself: we all started in a similar place not even knowing what we didn't know yet. You sort of poke and play and build some bad automations. Then you start to research new projects and start to learn what you don't know yet. That's OK: its a roadmap to future knowledge.

In my rig, I use HA to solve problems or address nuisance situations around the house. Wife and kids are forever leaving doors open with the HVAC on. I programmed HA to watch the HVAC (ecobee thermostat) and the states of the windows doors. If a door gets left open for more than 10 minutes, HA starts flashing lights as an indicator for someone to check notifications. After 20 minutes of the door/window being open, it turns off the HVAC and sends a push notification to my phone that someone is being a dumbass.

Another one is to shut off the basement lights at 10pm because the kids never remember to after they're done gaming down there.

Eventually you want to do.more sophisticated things, and that when the rabbit hole gets real deep.