With all the photos in photobucket, you should be able to see lots of small previews of all your pictures, something like this;
Beneath each picture are a selection of codes for putting the image in various places (websites, forums etc). The one you want is the IMG one, likely the bottom one, as so
If you click once on this, it should highlight the code. Then right click on the highlighted code and select copy (or with the code highlighted hold down the Ctrl key and press "C")
Next, go to the forum and right click in the new post area, and select "Paste" (or Ctrl and "V")
You should see something like this;
You can then click on the "preview" button below to check that the pictures are showing.