Enumerate the ! and [] usage in Access VBA?

Enumerate the ! and [] usage in Access VBA?

I've read several books on Excel and Access VBA already, but I'm still not
quite clear about the usage of [] and !, eg. like the ! in the third line
in the following code.
Can anybody generously enumerate some examples of how to use [] and !.
Sub modApp_ListTempvars()
' Set some example temporary variables
TempVars!FormName = "frmScreenForm"
TempVars.Add "Current User", Application.CurrentUser
' list all values for temporary variables
Dim tv As TempVar
Debug.Print "Listing TempVars" & TempVars.Count
Debug.Print "________________"
For Each tv In TempVars
Debug.Print tv.Name, tv.Value
Next
End Sub