The Manuscripts editor includes so-called "gutter helpers", designated with the blue + and o symbols in the left margin for the currently active paragraph. These symbols are buttons that lead you to shortcut actions for inserting (the + symbols) and manipulating (the o) the document contents in a way that is contextual.

The gutter insertion helper (+ symbol)

Gutter helper menu for inserting

The gutter selection helper (o symbol)

The following example shows what the gutter selection helper tool presents in the case of a paragraph.

Gutter helper menu for manipulating selection

The gutter helper is however entirely optional and can be toggled on or off from the Editing Preferences by choosing "Show smart gutter in the left margin when editing".

Preferences > Editing