The functionality exposed by blogs to members is controlled via permissions and configuration options. The default permissions for blogs within a group can be managed by navigating to the group, Manage > Manage Group > Permissions and reviewing the blog permissions granted to a specific role. To manage the configuration of a blog, go to the blog, Manage > Manage Blog and review the options there. To manage permissions for a specific blog, navigate to the blog, Manage > Manage Blog > Permissions.
For more details on managing permissions, see How do I manage roles and permissions to control what members can do on the community?