To attach a file to a post, simply copy and paste the file, in to the editor.
From the Attachments (paper clip icon) toolbar button in the editor you can also select an previous uploaded attachment, or upload a new one.
What files types can be used? How large can attachments be?
In the attachment window you will find a list of the allowed file types you can use. There may also be an overall quota limit to the number of attachments you can post to the board.
How to add an image to a post?
If you have uploaded an image as an attachment, they will be automatically generated a thumbnail that will displayed in your message, with an Link to the Full Size Image
To include an image that is not uploaded as an attachment and is located on another website, you can do so by copying the full URL to the image, (not the page on which the image is located), and either pressing the 'Insert Image' icon or by typing [img] before the URL and [/img] after it, ensuring that you do not have any spaces before or after the URL of the image.