Unable to make different meta descriptions for added Tumblr page -

There is some time at the end to work on some SEO on my Tumber blog. On my main page, I have this meta Tag is

  & lt; Meta name = "description" content = "{MetaDescription}" /> Now, when I made my new page, "About", "Portoflio", etc., I clearly want to make different details for these pages. But the tags above are automatically added to my new pages. Is there a workaround on this? Or am I not doing this right? 
 
 EDIT: I forgot to tell ... what I want in my other pages is not to take a snippet of the contents of the page. I have specific small details that I want to use. But with the above tag, it automatically takes the snippet.