A lot of people here are a little inexperienced with BBCode so I'll help you guys out.
How To Post Pictures
1. Find your picture off the internet or on your device.
2. Go to a photo hosting site (ex: imgur)
3. Upload your photo
4. Copy the link
5. Type [ img ] paste link here [ /img ]
6. You've got your image.
There's also a shortcut where you can just copy the link from another site and paste it, but it makes that domain owner have to pay an increased amount for bandwith. I rarely do it that way, as it just seems wrong to me, but if you wish to, I'm not stopping you. I just feel it's morally wrong to make someone pay for that. Anyway, those are two ways to post images.
How To Post Videos
1. Find a video uploading site (YouTube, Dailymotion, and Vimeo should all work in this website. For other websites, I do not know)
2. Copy the link of your video
3. Paste it in your post
4. You've got your video.
A lot easier with videos, because they're already sucking bandwidth even on their own page so it makes no difference. Plus the people who run those sites are so rich it doesn't even matter.
I hope this helps since some people can't seem to post these correctly (this is for you, Ben Kenobi!)