I recently got a few (5) hard drives to turn my home server into a NAS with trueNAS scale and my idea is to have 4 usable and 1 for redundancy, my question is… How does RAID work, like what is RAID 0, RAID 5, software RAID etc, and does any of that even matter for my use case?
That is a way too broad question to be answer here and also depends on the file-system truenas uses.
If I remember correctly it uses ZFS by default and you can easily find some articles explaining the different raid levels of OpenZFS online.
Edit: ZFS is not the same as other file-systems so not all of the general RAID info you can find online is 1:1 applicable for it (same with btrfs).