If the images are loaded into a file sharing program like photobucket, right click on the image and in the properties it will give the address of the image, highlight and copy.  Click on the insert image button when writing your new post, copy the info in between the two [img] boxes.

Otherwise click on 'additional options' below the box you are typing your new post into.
It gives you the option of attaching images from your hard drive by browsing and selecting the one you want, there is a max attachment size of 256kb

Clear as mud, right!