go down to the post reply icon towards the bottem left. then type what ever msg you want and then click on add attachment, then bellow that will appear a button saying browes, click on that and then choose the photo from you computer that you want to post click on the picture and then click open then you will see the name of the file/picture you have chosen next to the browes button. then click submit at the bottem and thats it.
i hope this helps and doesn't make it seem more complicating then what it is.