There are two cases
Case 1 : If u would like to post an image from any website ( I mean which has already a link). Copy that link and use the code given in the picture. You can see Paste your link Here in that picture. Copy the link and paste it.
Case 2 :

If you want to upload picture from your PC..then visit http://tinypic.com/ upload ur picture and copy and paste the html code.

Hope you got it. :)

Cheers.