So how do you insert an image?
What Zack said should work but you won't be allowed to publish the result on this forum.
Seriously though, you'd need some place in the internet to save your image to. Almost any server will do, doesn't need to be a dedicated image cloud service. There's lots of free alternatives. Do some googling for "cloud storage" or "image hosting" and read a couple of reviews to find yours. Look for limitations like how many times your image can be viewed daily, you don't want those. - Some ISP's provide "free" storage for your own site which works well too.
After having found a place to save your images, you might like to do some adjusting. Some image services might do that automatically, some won't. The idea is to make the image small enough both to fit any screen and to reduce the download time. Again, there's lots of tools for that for the unbeatable price of free. I like
Image Resizer, but there's even
online services for less frequent use.
Now that you've got your images on a server, re-sized for convenient use, you'd need a link your image. Often a right click on the image will give you an option to copy the address of the image. You then select the "insert image" button from the left side of the toolbar above your current message and paste the address between the bracketed [ img][ /img] commands. Post your message. Voilą!