You said: "Click on the note tab for any SOURCE and type something."
I think you meant to say: "Click on the note tab for any FACT and type something."
Text in a FACT Note will show a 1 in the "pencil" column. It can also be included in a Genealogy (Register) Report.
Text in a SOURCE CITATION Note will not show anywhere, in any other view or report that I know of. A SOURCE CITATION note is a "hidden" note.
I suggest not putting stuff in a SOURCE CITATION note for that reason. I suggest you use 1) the Fact note or 2) even putting text into Notepad and attach as a media instead. Or, 3) if very brief, into the SOURCE CITATION TEXT. Or, a final option, is to put the text into the Person Notes, under an appropriate hedaing.
An advantage to putting the source textual info in a Notepad file and attaching as a media file is that it is instantly available when you use that textual info as a source for other people. For example, an obituary in a Notepad file that names the parents, wife, children and grandchildren of a person is instantly available in any othese person's pages if it attached to a source citation as media. You have to go back and find the deceased person if it is put in as a Fact Note. But, the Fact Note can be printed in a Genealogy Register Report, a Source Citation Media item can't be printed.
So, I put obitary text in both places: a Fact Note and a Notepad file attached to a Source Citation. Ditto biographies that include genealogical info.