To include a picture in one of your posts it must be available on the internet in some location. It can be in one of the "gallery" forums on TM or some other web site, private or photobucket.com. The size of photos is probably best at around 800 x 600 which is large enough for viewing but not too big.
If using MS Windows you can navigate to the image on a website and then right-click (using the right mouse button). You will then get a pop-up menu. Left click on "Copy image address" (or words to that affect depending on the browser.
You will then have something like "http://blog.bradley.it/wp-content/gallery/morgan/img_4521.jpg/" in the clipboard.
When creating your post click on "Enter an image" icon (4th from the left above the text input panel). Choose one of the options then right click in the text box and choose paste (note that you must either cancel or over write the existing http:// prompt).
Here is the result
To post your photos in one of the galleries on TM or in photobucket I suggest you print out the "how to" post given in Simon's link above so that you have it available to follow while you post your pictures. Remember the maximum file size allowed is 1 MB and partly for that reason I have suggested a size of 800 x 600.
I hope that is reasonably clear.