1. First find the image that you would link to link to. Like this one of me in a moment of glory

2. Then click on the thumbnail in order to see the whole image. Once you are looking at the original image Right Click on it and then click on "View Image" on the menu as shown on the above screenshot.
3. Now click on the URL (as per the above screenshot) to highlight it. Then R click on it and click on "Copy". You can now paste that URL between image tags on the forum to have the image appear in your post.
4. When you will be writing your post on the forum click on the "Insert Image" button as per the above screenshot.
5. You will see "

" tags appear in your post where you had your curser at the time of clicking the Insert Image button. Now all you have to do is Paste the URL between the brackets and you are done

If you don't currently have a program that allows you to edit/resize photos then I recommend GIMP
http://www.gimp.org/ This is the software that I use for everything on this website. It is free and since I have been using it for a long time now you always have someone you can ask questions.