Help wrapping my head around the idea of SharePoint online.

A good place to start is to compare on premises to cloud and the pro’s and cons of each. Here are some resources to help

https://gallery.technet.microsoft.com/office/SharePoint-On-premises-Vs-b51ac06e

https://sharegate.com/blog/sharepoint-on-premises-vs-sharepoint-online

https://www.contentandcode.com/blog/sharepoint-online-vs-on-premises/

By moving to cloud you lose some things and gain others, but arguably the level of management in terms of sites, lists, web parts, and permissions are similar. Indeed, I would recommend a trial of office 365 so you can setup an environment away from your production to simply play around and compare features before setting up anything which may impact or be visible to users.

From a business perspectives the big reasons to move to cloud are cost, evergreen and the integration with the rest of the 365 stack

I would also consider looking on places such as YouTube, Pluralsight and Udemy too for SharePoint Online courses. In addition there is also the option to use both and have hybrid SharePoint which could also be an option

Hope this gets you started to help make a decision, and answers your question.

Best, Chris