Don't feel bad. I'd go as far as to say that this is a recurring issue for all/any internet forums. The problem appears to me to be that many who begin posting in forum don't have much experience in computers, while those who set them up originally assume that their users will be as computer/internet savvy as themselves (for the record, in the past, that may have been the case).
Click on the image icon above the large text entry box, the one where the hovering text shows "insert image".
1) From Computer: Uploads image to the forums server (AFAIK). Follow the steps to finding your compressed images on your computer's hard drive.
2) From URL: Forum software accesses your image from an offsite server, most commonly your own website host's server. You need to provide a complete Uniform Resource Locator (URL), a "path" to your image. The URL must be exact. You can obtain URL's most easily by copying the internet address line at the top of a window, or from your file transfer software (needed if you set up your own website). It looks like this:
- rangeoflightphotography.com = my website domain name
- /albums/Eastern-Sierra = the folders where the image can be found
- Sunset%2C%20Sierra%20Crest.jpg = the image itself
or may be entered directly by html command line in some forum software:
resulting in this:
The second method is preferred as it doesn't use the forum host's server space, isn't limited, and allows you to retain control over your images.
Sharing from flickr accounts requires allowing access via license establishment and then getting the embed HTML code from flickr (I can't give an example because my spartan flickr account is all rights reserved).
In both cases it is best to keep images small, probably jpeg, at 72DPI and not much more than 100KB, to ease host space and transfer times (download speeds) to the forum user. IMO, posting forum images that are so large that they take more than a fraction of a second to load at normal DSL speeds, or that are larger than the average viewer's computer screen (say >800 pixels), forcing horizontal window scrolling to view the entire image, is just plain rude. Use your image processing software, like Photoshop, or google on–line image compression.
The Link icon (world) and Insert Video (filmstrip), located in the same icon bar, work pretty much the same way, not only in forum software but also in website creation software such as Wordpress and other CMS (Content Management System) software. Here's an example from my YouTube Channel, another server:
Click Insert Video and enter the path:
resulting in this:
I am a big proponent of adding links and referential images to posts, when appropriate, especially in assisting to differentiate experienced advice from unsubstantiated opinion. IMO adding illustration and links is what livens up and prevents internet forums from being dull white paper and text, putting the "inter" in the "net".
Hope I'm not rubbing your nose in it...