A Blog functions as a container that holds individual Blog Posts. The Blog itself acts as a landing page, automatically displaying its posts in reverse chronological order (newest first). Each Blog Post includes a publication date, author byline, teaser text, and featured image. Blogs themselves cannot hold very much content, only an Intro (with Heading and Subheading).
Visually, Blogs are similar to Categories. The key difference is that Blog content is inherently time-based. If your content doesn't have a meaningful "when," a Category or Topic is likely a better fit.