you cant post a picture or any images on your topics/thread,  you need to rank up your account first to atleast junior member rank so you can use this feature and in order to do it you must upload your desired images to any image hosting sites like imgur,photobucket,ctrlq.org,etc ( i suggest ctrlq.org for i am using it all the time and no signup required )  then after you upload it , find and copy your unique image link and post it here with this code.   then you can see your image now. hope that it clears your mind.