Hi Dan, and welcome to the community!
There’s no openHAB client app to control Mac or PC devices, but I found a way to send some basic commands to a PC using IFTTT. However, I don’t recommend this as a starting point for your openHAB experience. More on that in a minute.
For Zigbee, I’d recommend getting a USB stick instead of using a separate hub. However, if you already have the hub then it might be possible to integrate it if there’s a binding.
The best advice I can give is to put aside all of the complex stuff you’re envisioning for the moment and start with something simple, such as an openHAB-friendly WiFi plug. Too often, people try to tackle significant challenges without having a good understanding of the basics. That’s like going on the highway in your very first driving lesson–it could go well, but it probably won’t.
What are you planning to run openHAB on? You mentioned putting a “ZigBee USB stick in the PC”, which makes me think that you’ve installed it on a Windows PC.
openHAB will absolutely run on Windows, but there are fewer people doing that in the community so there will be times when the help you receive will be limited. Whereas if you run openHAB on a Linux computer, there will be lots of help available. Going even further, many of us use Raspberry Pis with the preconfigured openHABian image, which enables you to quickly get into items, rules, sitemaps, etc. It’s a great way for beginners to start out with lots of help from the community.
Cheers!