You can have pictures in your posts 2 ways:
1) Attach pictures to your post and upload them to the forum OR
2) Reference pictures elsewhere on the web within your post

1) To post pictures in the forum use the Browse button in the "Add an Attachment" section of the Post screen and select an image file from your PC to upload.

This will upload a picture to the forum and attach it to your post. You can have 5 pictures per post.

Please make sure your pictures have been properly resized so they are not too huge.

2) You can also have pictures which are already hosted on the internet somewhere appear "inline" inside your post text using the "Img" button. It will put image tags into your text like this: "[img]URL%20of%20your%20picture[/img]". For this to work your picture must already be uploaded somewhere on the web.