If the person already has a City Blogs account, you can add them to your blog.
For a full breakdown of the roles please see the Edublogs guidance on roles.
If the people you want to add don't already have a City Blogs account, you can generate an invitation and e-mail it to them. When they accept the invitation, their City Blogs account will be created and they will be added to your blog. They must have a City IT account.
Your blog Dashboard also displays recent comments. If you are viewing your blog, you can see a count of the number of comments for each post and selecting on the number of comments opens these for you to read.