Good question. Unfortunately, I do not believe there is an easy answer (without scouring the Internet 
) There are many YouTube channels that might be helpful. 
What types of devices are you interested in adding to your home automation system? What do you already have in your house?
Broad categories would be things like:
- In Wall Switches, Dimmers, and Fan Controllers
- Smart Bulbs
- Smart LED strips
- Sensors
- Motion
- Contact
- Leak
- Temperature
- Humidity
- Vibration
- Illuminance
- Human Presence/Occupancy
- Air Quality
- Smoke/CO
- Geofence-based Presence Sensing
- Window Covering Automation
- Garage Door Automation
- Infrared device control (e.g. television, receiver, media streaming box)
- RF device control (e.g. ceiling fan)
- Voice Assistants
- Amazon Alexa
- Google Home
- Apple Siri
- Home Assistant’s new local voice assistant (this is The Year of the Voice!)
- Video Cameras
Once you know what you’d like to automate, then you’ll probably want to think about which type of connectivity to those smart devices will work best for your needs. Typical choices are:
- Zigbee
- Z-Wave
- Wi-Fi
- Matter over Ethernet/Wi-Fi
- Matter over Thread
- Lutron Clear Connect RF
Cloud Connected versus Local?
How robust is your current home network/Wi-Fi system?
Custom devices (e.g. ESPHome) or Off-the-Shelf?
I know I have not really answered your question as to where to go and find all of this information. Instead, I hope I have not overwhelmed you with even more questions to consider. Early on in the journey is a very good time to tackle these questions to set yourself up for long-term success and reliability.
My personal preferences, from over the past 25+ years of using many products from many vendors, has resulted in the following list of device/vendor selections. Note: I am in the USA, so not all products may be available in all regions of the world.
In-Wall Switches, Dimmers, Fan Controllers, and Button Controllers
- I use Lutron Caseta for all of these devices. Lutron is well known as one of the most reliable solutions, has excellent customer support, and works with most every other home automation system on the market in the USA. It works directly with Amazon Alexa, Google Home, Apple HomeKit, Logitech Harmony Hub, Home Assistant, Hubitat Elevation, SmartThings, etc… While not the cheapest solution, it has been 100% reliable for my needs. It does require another ‘hub’ for all of the Lutron Clear Connect RF devices to communicate to other platforms over your home Ethernet network. I use the Lutron Caseta SmartBridge Pro2 for this task, as the “Pro” version offers the most flexibility and integration options.
Smart Bulbs
- I use a Philips Hue bridge + genuine Hue bulbs. The Hue bulbs have the advantage, when connected via the Hue bridge, of being able to return to their last state after being powered off and back on. Many bulbs simply turn on to 100%. Genuine Hue bulbs also are required for native Apple HomeKit support. Hue works directly with Amazon Alexa, Google Home, Apple HomeKit, Logitech Harmony Hub, Home Assistant, Hubitat Elevation, SmartThings, etc… While not the cheapest solution, it has also been 100% reliable for my needs.
Sensors
- I use Zigbee sensors for Motion, Contact (i.e. door and window), and Leak detection. The ones I use are older Lowes Iris v2 sensors OEM’d by Centralite. They have excellent battery life and are very fast at reporting status changes. Unfortunately, the exact models that my house is full of are no longer manufactured.
- I have been pretty happy with an Aqara FP2 human presence Wi-Fi sensor. It allows a room to be divided up into multiple zones, with each one reporting whether or not a human is present in that space. It takes some time to get configured, and may not be suited for all user environments. YMMV
Voice Assistants
- I use Amazon Echo devices throughout the house.
- I do have one Apple HomePod Mini that I use for mostly testing out Apple HomeKit/Siri functionality.
Smart Speakers
- I have an IKEA Symfonisk speaker, which is made by Sonos. It handles Text to Speech duties for making announcements, like when the mail is delivered to the house, or when someone is at the front door, etc…
Infrared Remote Control
- Logitech Harmony Hub with remote. Unfortunately, Logitech no longer sells this device. Fortunately, their cloud services still support it as necessary for configuring it to handle new devices. I am hoping that something comes along to fill this void in the future. Nothing else, thus far, seems to be as reliable and capable.
Media Streaming Boxes
- I have an AppleTV box at every TV in the house, which provides a clean, consistent, ad-free UI everywhere.
Video Cameras
- I use Ubiquiti’s UniFi Protect Cameras and NVR solution. I use UniFi for all of my home network switches, access points, and router functionality.
I hope this helps you on your journey. Lots of folks with many, many years of history frequent this community, and others. So, asking questions, and possibly focusing on one particular automation goal will probably help to close in on a solution. But, keep the big picture in mind as well so as not to paint yourself into a corner, so to speak.