Post Tags are like a Post Index
Unlike Pages, which have a menu access, timeline Posts have Tags, very brief one-word or short word-string description which serve to “index” the content of the Post.
Tags using Two-Word combinations are often the easiest way to zoom in on a post content
Example: I did a recent post on “page hierarchy” : Where there is a Parent / Child relationship between two pages. Logically enough the tag was then “page-hierarchy”, reflecting a parent-child relationship as well