Key Point:
A Gallery Forum is simply a forum that allows you to upload Photos. Adding a Photo is very similar to the way you Add a Topic for text posts in other forums.
In a Gallery forum click the Add Topic link.
Below the Body section, click the Manage Files link. (See first photo)
A window will appear allowing you to upload a file. Click Browse and select the file from your computer. Then click Add.
Review the file you added at the bottom of the window. When you are done, click one of the blue icons on the left. (See second photo) This will insert the code for the photo. Click Finished to add the file to your post.
If two photos appear in Preview mode this is normal.
You can add text to your post in the usual manner. Text will appear below your photo.