I'm new to LyX. How can I achieve the list style reflected in the second picture?
Description in the standard
article class typesets as you desire, but the typesetting changes according to document class.
So: Change your document class to the standard article, or redefine how the
description environment is typeset.
If you are working in the standard
article document class, then the
Enumerate environment typesets as you want.
So: Change the environment of your list from
Description (?) to
If you want the items labeled with something custom, then go
Insert > Custom Item when on the line you want to change the label of and then write your desired label in the resulting box. In the screenshot, I didn't bold the text, but bolding it works, too.