There are two ways to use attachments, "in line", that is within the post, or in a box at the bottom of the post.
To upload attachments, click the paper clip icon at the top of the text entry area or the "Manage Attachments" button below it. You may specify URL's or files on your computer or a combination of both. Only four attachments are permitted per post.
Once you have entered the locations of the files, click the "Upload" button. When the file are uploaded, you can close that window.
To have the files appear at the bottom of the post, you need do nothing more. If you want them in the middle of the text, place your cursor where you want the attachment and again click on the paper clip icon above the text entry area. You will see a list of uploaded files. Click on the one that you want and it will be inserted between a pair of [ATTACH] tags. There is also an option to select them all at that time. Any that are not inserted into the text automatically appear in the file attachment box at the bottom of the post.
An "in line" attachment below:
battle_3kharkov SS Panzergrenadier troops of Leibstandarte SS Adolf Hitler in Kharkov, Mar 1943.jpg
from the Battle of Kharkov in March, 1943
And below in the "attachment box" is a photo from Stalingrad.