The newest Echo (and possibly Dot?) has a smart hub built-in, previously they didn’t so it wasn’t so much an advantage, it was a requirement to buy a separate smart hub. I can’t see a need for a separate one now unless the one built-in to Alexa doesn’t support the devices you want to use.
I have a v2 Dot (without builtin smart hub) so for lighting I bought a Phillips Hue Starter kit (includes the hub + 3 bulbs). You need to register the hub in the Alexa app and then register the bulbs in the Philips Hue app. I had to create the rooms in the Alexa app to (otherwise she doesn’t recognise them, at least without some added Skill word). I’ve actually over-complicated my set-up as I have 4 different apps now with config in them and I have no clue what is actually the master now :p
But basically you create a “Living Room” room and register the bulb you’ve plugged in there to it (they get discovered by the app). Then you just say “Alexa, living room on” or “Alexa, living room 50” (this sets it to be 50% brightness, turning it on in the first place if it’s not already on.
Then there’s scenes and timers (I’ve only created one timer/schedule so far so my bedroom and living room lights come on gradually starting at 5:35am (10 mins before by alarm goes off) and switch off at 7am (just after I leave the house), on weekdays only (the last bit is important as I found out waking up the first Saturday I set it up with a hangover to glaringly bright lights :p ).
I haven’t got into controlling other stuff yet, I did look briefly at it and there’s various stuff such as a Logitech controller but reading about that it seemed overly complicated and not fully supported in the UK. I gave up looking at that point but I’m sure others have a working setup…