In Libreoffice terminology, this would be a nested list.
You can do this manually by adjusting the paragraph style (select text, right-click, select "Paragraph," then see "indents and spacing" and "bullets and numbering").
Better would be to create a style to use and apply that style to the text in question. Trying to explain how to do would be a complete tutorial, well beyond what I would wish to attempt in a forum post, but Ahuka has
series about Libreoffice at Hackerpublicradio.org.
This one seems to be the particular one addressing that subject.
You can also see
the Libreoffice help.