Hi Sue, I have seen this question before and as far as I know your web hosting company needs to enable this facility (if they offer it). Have a search through the Q&A to see if you can find another post on it, or wait until someone who knows more than I do to answer.

Dear Sue, 

do you mean comment on your blog posts or do you mean creating a blog article?

In the first case you need to enable the comments and choose the way to manage them:

http://help.websitex5.com/en/v14/pro/blog_tab3.htm

http://help.websitex5.com/en/v14/pro/blog_admin.htm

In the second case, you always need to use program to edit or write new blog posts, then export the website again, as it is unfortunately no possible to do this online. 

Please let me know if I can help you further. Kind regards.