The Blog
Writing posts, categories, and linking posts to the products they are about.
Blog, Posts. A blog on your own shop, under your own address.
Why Bother
Two reasons that hold up. It gives people a reason to arrive who were not already looking for you, and it gives you something to link to from an email or a social post that is not a product page.
A blog nobody updates is worse than none, because a shop whose latest news is eighteen months old reads as a shop that may have closed. If you are not going to post, do not show it.
Writing a Post
A post has a title, a slug, a body, an excerpt, a featured image, categories and a published date.
The excerpt is what appears in listings and in search results. Left blank, the start of the post is used, which is usually a worse summary than one sentence written on purpose.
The featured image is used on listing tiles and when the post is shared. A post without one looks broken in a row of posts that have them.
Published date can be in the future, which schedules it.
Categories
Blog, Categories groups posts. Keep the list short, for the same reason as product categories: a reader will not use fifteen of them.
Linking to Products
The most useful thing a blog does for a shop is send people to products. Link to them from the body of the post, in the words somebody would click.
A link to a product that moves will break
Product addresses change when a slug is edited, and an old blog post then links to nothing. If you change a product slug, add a redirect so the posts pointing at it still work.
How the Blog Looks
The writing is on this screen; how it is presented belongs to the theme. Settings, Appearance, Theme Settings has two groups for it.
Blog Listing governs the index and the category pages: whether articles appear as rows or as tiles, how many to a row and to a page, how wide the page runs, whether the category sidebar shows, the shape of the images, and whether each article shows its excerpt, categories, author, date and reading time.
Blog Post governs a single article: narrow or wide, the featured image, categories, author, date, reading time, share links, links to the articles either side, and how many related articles to show.
Which choices exist depends on your theme. A theme decides whether it can draw tiles at all, and one that cannot simply does not offer them.
The excerpt length is a setting
If your excerpts are being cut mid-sentence in the listing, the cut is Excerpt Length under Blog Listing rather than anything wrong with the writing.
If Your Blog Lives Elsewhere
Many shops already have a blog on another platform. A theme can pull posts from an external blog and show them on the shop instead of using the built-in one.
In that case the posts are written there and only displayed here, so scheduling, categories and images are managed at the other end. Anything about pinning or ordering posts has to be done there too.
What to Write
The posts that earn their place are the ones answering a question somebody actually asked: how to choose between two things you sell, how to look after something, why one edition differs from another.
The posts that do not are announcements of things only you care about.