I just followed the instructions on the graphene website and it was super easy. I used two phones for a couple of days just to make sure I had all the stuff I needed access to for work etc but stopped taking my iPhone with me this past week. Side of Burritos on YouTube has some good content as well.
Discussion
I am too nervous that i will end up bricking my phone.
If using our web installer you can't, so long as your bootloader is accessible you can put an OS on it.
The advice received above about just following the official guide is paramount. Do NOT use third party videos if possible, USB debugging is NOT required.
Any problems let me know or visit our support rooms:
GrapheneOS Community https://matrix.to/#/#community:grapheneos.org
Give it a go, let the inner power user free.