Short answer
In Content > Blog, the Configure menu holds Blog listing pages, Tags, Comments and Authors. On the Blog tags page, click Add new tag. In each post, pick authors from the Author dropdown and add tags in the post settings. Tags create tag listing pages, so a short, consistent tag set keeps those pages useful.
1. The Configure menu
In my demo portal, the blog posts list with Configure open.
2. Keep tags tidy
- Merge near-duplicate tags before they spread.
- Give authors a bio so author pages are not empty.