You’ve come to the right place. A lot of knowledgeable members on here that can guide you along the way.
First things first. What are your ultimate plans? Basic in home control on your iPhone or out of home with automations. If the latter, then start out with a Home hub, if you don’t already have one. An AppleTV, HomePod or stay at home iPad. From there, it’s really simple. All you have to do is hit the + button and then add accessory. Every (official) HomeKit accessory has an eight digit code and/or a QR code. Just follow the on screen prompts and the accessory will show up as a tile in the Home app. From there you can add scenes which are basically multiple accessories controlled under one button. Automations are user written rules to trigger accessories based on an event.
Everything in the Home app is pretty intuitive and self explanatory. It may not be reliable sole of the time but it’s definitely user friendly.
There is a YouTuber named Shane Whatley who made a ton of HomeKit videos ranging from very basic set ups to very advanced using shortcuts. Lots of product reviews as well.
Please don’t hesitate to ask more specific questions. While simple, I could probably write a whole book on HomeKit from top to bottom.