Simply follow these 4 steps (2 images):
1. Click "Image Library
2. Click Galleries
3. Choose Default Gallery
Then...
4. Scroll to the bottom of "Default Gallery" and fill in the fields seen in the image below:
To add the image to the forum post "Right Click" on the image in the gallery, click on "Properties", Highlight the "Address:(URL)"- (http://...) - and copy. Then go to the location in the forums for your post, select "New Topic" or "Post Reply" and in the Edit Box bars at the top, in the second row is an icon with a mountain in it - click it - in the top "Source" box right click and paste the URL in it, click in the "Image Description and at least hit the spacebar (it alleviates issues).
If you need to resize the image - click the image - you will see small white corner squares appear. Hold down your left mouse button on a corner (not the sides) and pull it towards the middle of the image to the desired size and let go. Type your text around the image, preview and submit.
Good luck,
JT