If you are used to an OS such as Winodws or Mac, then Linux is a pretty steep learning curve. It took me a few days of reading and getting it wrong and reinstalling Raspbian more than once to work out what was happening. I installed RetroPie from the manual install script a couple of times as well. You won't damage your PI but maybe get frustrated and banging your head against the table trying to work out what won't work and why
There is quite a bit of manual installation even after getting RetroPie up and running. Linux is a good OS but needs a fair bit of user assistance to get it running how YOU want it to run, especially in allowing access to various parts that you normally wouldn't be able to access to give you more control over it
Once it is running, RetroPie is a breeze to use and very simple to add to as and when YOU want to including adding or removing ROMs or emulator systems, unlike Windows that constantly badgers you for yet another security/software update (especially Windows 10 that has taken ALL the control away from the user when updates are needs .... or that Microsoft believe is needed)
Did you read this guide, it helps a LOT
https://github.com/retropie/retropie-setup/wiki/First-Installation