Assuming you're trying to upload a picture from your PC. If so:
Whether a reply or new post, click in the Message block where you want the picture to appear. Make sure there's at least one space separating whatever you've already typed and the place you're putting your picure. Then click the "Upload Image into Post" button
Make sure your filesize is less than 2mb, not a .bmp image, and preferably .jpg format. Click Browse
Here you can see the file is .jpg and is only 15K. Click your file once to highlight it, then click "Open"
Takes you back to this window where you just click "Upload"
Now you will see the "code" needed to display your photo. Everything between the arrows, including brackets is needed. Add additional text either before or after this stuff then click "Add Reply"
Be aware that you'll only get this kind of instruction on this site!