A channel is where blogs created, blogs followed, and posts from blogs followed by a particular user are listed. Channels are by default publicly accessible but the visibility can be changed from settings. 

Note: Setting channel visibility to anything other than the public, may prevent more people from finding your blogs. 

A blog on the other hand is more or less like the normal blogs you are already familiar with on the internet. It's a customizable platform where users can create and publish blog posts. 

As a blog owner, when someone subscribes to your blog, posts from your blogs will begin to show on such users channel thereby increasing visibility for the blog and posts from the blog. It's a good practice to encourage more users to subscribe to your blog so they as well as the people who visit their channel can see your future posts on the subscriber's channel.