OK, Open photobucket,click on pic you want to post,upper corner of pic will be a gear looking icon,click on it,window opens ,click on "Get links",bottom of list is "IMG Codes",click on that,It will highlite yellow. You have just copied the pics img code .
Now go back to forum and click on reply or new topic,go to top of screen to EDIT,from drop down click on paste. You have now pasted the img code of pic to forum. To check if you did it right click on "preview reply" and PRESTO! a picture.GOOD LUCK