I would check out the free recorded technical sessions from the various conferences. They have all levels and some are very recent. More are added all the time (i.e. after the July User Conference...probably available in August)
E360 Video Search | Esri Videos youtube also has a channel esri - YouTube
Looking on the main https://www.arcgis.com/home/index.html page, there is a link to Learn ArcGIS that you can check out.
You may want to check out The ArcGIS Book which was release a couple years ago. (sorry, I haven't used it myself)
There are MOOC (Massive online ..OC?...training classes) that are free too. Self paced, but over about ascheduled 6-week period usually. Here is an older blog, but it will lead you to more
Earth Imagery at Work free online MOOC from Esri | ArcGIS Blog
And I guess you have already checked out https://www.esri.com/training/arcgis-online-training/
Some of these may be a year old, but they are still good for getting started.
But the best way sometimes is just to jump in and try things. However, I would suggest limiting the number of credits an individual can use so that if they click on something to try, which eats credits, it should warn them and/or limit (crash?) if they try to geocode the world, for example.
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