New to computer audio

I'm looking at purchasing a Roon Nucleus and was wondering how to transfer the files on my computer to the internal HD of the Nucleus or if that is possible? Can one use an external CD ripper to transfer CD's to the Nucleus as well?   Also, are most users connecting their Nucleus to the amplifier via a DAC.

Probably simple for most of you but I'm new to this and want to make sure I can get access to the10K of songs I already have on my Mac.

Thanks