Essentially it's a 3-step process:
1. Upload your picture onto a web server that provides a hosting facility. There are bazillions out there to choose from, Tm-img is ours and is free to use. Here's the address:
https://www.tm-img.com2. Copy the url of the picture to your clipboard. tm-img makes this easy by providing a BB-Code format link in the 'Embed Codes' section
3. Paste the link into your post