Lovelace modes

Nube here, getting nowhere fast! (Using HAOS on Proxmox if it matters. . .)

I’ve installed HACS, tried to add a few custom cards. I keep getting what appears to be an error message:
"After the download completes, since you are not using Lovelace in storage mode you need to manually add the resource with these settings:) I’ve done that to the configuration.yaml file and have gotten the OK from Check Configuration.

Also confused: in some places it seems that there are three modes: UI, yaml and storage, yet other times seems like only two are referenced.

So, am I missing something? The way the line above reads seems to imply that I should be using Lovelace in storage mode(?) If so, have not found how to do it after spending several hours searching this forum and help from google.

tia