There are a two ways to do this so I'm going to explain both of them.
This way shows you how to upload it as a link. You'll click on the link here and click on browse. You can click on the photo you want and it will go into the space. Then you copy the link from the website and can post it in a thread.
This way shows you how to upload a photo. This will make the attachment be at the bottom of your page. While you're writing a thread, you can click on the button in the middle that says "Upload a File." It's between "Post Reply" and "More Options..." Click on that and press "Choose." You will then be given a list of options, press on whichever one you need and then click on the picture. It will put itself below the post and when you click "Reply" or "Create", it will be under the post.
If you have any further questions, feel free to message me or another staff member.