blue dot when Editing

[William Anderson]

what is the blue dot on left side when editing

[Eko palypse]

@William-Anderson

might be the visual representation of a whitespace char.
Goto menu View->ShowSymbol and check/uncheck those
to see if it is.

[Meta Chuh]

welcome to the notepad++ community, @William-Anderson

if you mean blue dots on the left, next to the line number, as seen at the screenshot below:

those are bookmark points.
you can set them and remove them by clicking inside the grey area between the line number and your text/code.

they are very helpful, if you have a text or source code file, where you have to scroll up and down repeatedly.
so if you are working on line 20 and line 2000 at the same time, and you want to switch back and forth between them, you just have to press f2 to jump to the next bookmark, or shift+f2 to jump back to the previous bookmark.

there are many more features for bookmarks, you can see some of them at the screenshot below.