What is feed url & viewing url in creating a blog?

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Oh, me again. I just want to start my blog.But when i try to fill in the 'creat a blog' sheet, i am coufused at the items 'feed url'&'viewing url'. What are they? I refer to the dictionary and can't find any suitable explaination of 'feed' in this 'feed url'. Friends , i really need your help. i am waiting...