How Do I Create A Session Value From Html Anchor Tag Click And How To Get The Session Value In Aspx Page

What do you mean by "redirecting"? To you mean the html page has a link that links to an aspx page? You can't do anything server-side between the client event and the aspx page being requested, all you'll be able to do is use a synchronous ajax call on the click event of the link on the html page to call a service\webmethod on the target aspx site to pass some data which is held in the session. After the call happens the aspx page is then requested and it should be able to read any data stored in the session by the previous call.

If you can't amend the html page then there is nothing you can do, you'll just need to do all the work on the target aspx page. It's a strange thing to want to do, maybe if you explain what your ultimate goal is someone can advise further.