Don't know exactly what you did or what you are asking because the terminology is incorrect.
We IMPORT image/video files INTO Lr Classic CC.
We ADD image/video files to the Lr CC cloud ecosystem.
What does 'migrate' mean relative to your question?
In the new Lightroom cc, you can click on the + sign to add images, or you can go to FILE>Migrate Lightroom Catalog to import the catalog. One of the tutorials I saw said that if you just add images the adjustments made previously in Lightroom Classic are not imported with the images, but if you Migrate your catalog, then the images and adjustment data comes together.
I'm trying to get a better understanding of what the Migrate option to is.
Is it only to Migrate the lrcat? or is it for images as well?
Do you only add images with the + sign, or do you add images with the Migrate option too?
If you want to sent your entire collection of files that are in any Lr Classic catalog (you'll have a choice of catalogs), Migrate will do that.
If you want to send (sync) files not in a Lr Classic catalog to the 'cloud' use the Add feature.
Be sure to close Lr Classic CC before attempting a Migrate because the process can not send (Migrate) an open catalog.
> Is it only to Migrate the lrcat? or is it for images as well?
Both 'Add' and 'Migrate' include the actual images as same need to be synced to the cloud.
If you already have a Lightroom Classic catalog with collections, edits, keywords, etc, and you want to transfer all of the existing catalog contents to Lr CC, 'Migrate' is the better option. If you choose 'Add' then only the images and any embedded metadata will be addd to Lr CC catalog. As such, any collections you have had in Classic will need to be manually recreated in Lr CC.
Lr CC guides you through the migration process, and checks that there are no issues with the images or the catalog. The only catch being that any existing 'Lr 6 or 2015.x' catalogs already synced to the cloud will be disabled. That is, syncing will be disabled, the catalog and earlier version of Lr can continue to be used.
If still unsure then it would be worthwhile creating a small sacrificial catalog in Lr Classic, including one or two small collections / collection sets, then migrate this into Lr CC. This way any concerns you might have regarding damage to your current Lr Classic catalog are avoided.