How to put text just below to thread list in index page

I am trying to put an html code which would be actually an offer or ad which will appear in homepage just below to forum list.

Because I also have sidebar there appears a blank space on the left side below of thread list.

  gpgp.PNG (Size: 105.6 KB / Downloads: 2)

Tell me how to put the HTML code or suggest plugin if there is one for the same.