I will have a new email

I am soon changing internet providers which means my email address ID will no longer be valid. I need to change the email on all Apple and iCould IDs. I tried to use my iCloud email, which will now be my main email, but could not.

Anyone have a solution? Anyone have step-by-step directions? I am usually good at this stuff, but I've been reading other people's issues and now I'm really scared to try this!!!