How to use Attachments
Boy, basic things are hard oof
Clicking on "Insert Attachment #" placed a BBCode inside the post. The number is the ID of the attachment.
There is also
As comparison I did not place the 2nd attachment inside the post. Any attachment added to the post itself will not be displayed at the bottom of the post.
The Attachment=# tag places the full blown image inside the post (The mod does downsize the image a bit in case it's too big)
The Attach=# tag puts a thumbnail inside the post.
By default Attachment=# is used but you can shorten it to Attach=# if you want to use the thumbnail variant.