Are you trying to think of your main 3 topics for your pages?

What about

hair loss for women
hair loss for men
hair loss for young people

Or

natural hair loss cures
OTC hair loss cures
Prescription hair loss cures

You might start asking what do people who are losing hair want? Regrowth? Wig? Shampoo that will stop further loss? Confidence with hair loss? How to look good with no hair? Head polish? Spray on hair? Some ideas to get you going and some to make you laugh.

Each one could be a page with several posts.

Have a look at the link below...this should answer your question... What Are Tags And How To Use Them I hope this helps...

These are identifiers as to the subject of the post as Leo mentions, and they are also good for SEO, as Robert mentions...

Another use for them is they provide a quick way for a site visitor to get right to the point they are looking for on your website...

In my case, after posting articles, tutorials, training, reviews, and tips...I have many many posts...

I want site visitors to be able to get to the content they are looking for...The tags are included in a sidebar of my theme, so they can find the subject of interest easily...

This, of course, means that they likely will stick around longer on my site, start to get to know me, and maybe come back again...Then I would hope that they opt-in, etc...

Cheers!
Dave : )

If you are referring to writing a WA blog post.

The tags are words that would identify what your blog is about and is used for indexing within the WA, this way when people do a search here in the WA the search tool has a reference for the search inquiry.

I would think its the same as when you are writing an article.
You insert all the right Tags with regard to good SEO practice.

Title Tag, Keyword Tag, Description Tag and Meta tag.
My last blog dealt with the Meta Tag but the others are mentioned as well. Meta tag seo Enjoy your Wednesday.
Robert