To convince certain persons to shift from Clearcase to Git, I need to show them alternatives to the baselining and checking in/out documents under activity names.
How can these be achieved in Git? I only saw the tagging option coming into the picture in this scenario, but that seemed to be useful for creating version numbers rather than for baselining or activity names.
You can read in my old answer a good comparison of ClearCase and Git.
"What are the basic ClearCase concepts every developer should know?"
They key aspect to understand is that a Git repository would be the equivalent of a UCM ClearCase component: you cannot store all components in a Git repo like you could in an UCM Vob with the (centralized) ClearCase VCS.
Once you realize that, a baseline is just like a commit of your git repo: it will reference the full content of that repo. You can add a tag on it if you want (like a full UCM baseline), but it isn't mandatory.
Each commit represents an activity: the UCM activity is a "change set": a list of changes, which is what a Git commit allows you to find.