It's very easy to install when you just follow the steps of the web installer instructions on the webpage. As long as you got a working usb c cable (yuo probably need to try several) and the device is found by the installer, you can't do anything wrong.
If you made to install it, it's also very easy to go back to the factory stock android firmware.
So don't be feared to try it out, there is almost zero chance that you damage your phone.
Graphene OS is easy to use. You can install the Play Store and Play Services and then you can use all apps that are available on the official app store. Just some banking apps and some official government apps (but don't have to) might not run.
Google Pay doesn't work. In Germany you can use PayPal for wireless payments via NFC-this might be rolled out to other countries in the future.
The Google backup solution and find your phone don't work either.
Outside USA the RCS messages work fine since some weeks-its explained in the forums how to enable it.
All in all the OS is wonderful if you don't want any AI integration and prefer to have control which apps can connect to the Internet and what rights these are granted.
If you want AI features integrated into the system Graphene OS might be not the best choice. You still can use AI apps, but the convenience (or annoyance) of having AI built into the system is gone.
I would encourage you to try it out for some days. Start slowly. I would suggest for the start to use only the owner profile and to install the Play store and services.
If you managed to configure everything to your liking, you can do some research in the forums about the specialities of the Graphene OS and see which of these you find interesting.
Start with the apps you want to use daily, maybe messengers, email etc.
And if you aren't satisfied or feel like that you feel better with the original stock android firmware the Phone came with, then you can revert everything.
If you have questions just ask in the forum, in almost all cases you get answers within some hours.