Question: Amazon Tags

I am attempting to up my promotional game, and keep reading about Tagging on Amazon. Could someone explain to me exactly what the benifit of doing this practice is (I don't like doing thing unless I understand them).

Product placement? Product placement where? Or is this purely a random search thing. As in I search "fairy" and my book props up higher ... or lower if my tags are low?

My understanding: We have space for tags on our Amazon Pages. Readers can use these to note what themes/genres the book portrays. Other readers can agree/disagree by clicking on these. These tags then ....

Having a look around at other books my tag numbers are nonexistent, but this isn't impacting my book sales (is it?) Could someone break it down for me, please. Virtual high-five up for grabs.