Post Thumbnails
There are two methods to set your post thumbnails in Arras Theme:
WP Built-in Post Thumbnail (WordPress 2.9+) - Recommended
timThumb Script (Legacy)
The First Method
Create or Edit a post by clicking Posts › Add New or Posts › Edit.
If you are editing a post, select which post you wish to add a thumbnail in.
Under the Post Thumbnail meta box, click on Set Thumbnail.
Upload your image that you wish to use as a thumbnail (external images will NOT work).
Click on Use as Thumbnail.
That's it! You're done!
The Second Method
This method is still available for the sake of those who have upgraded from 1.3.x.
Ensure that you have set your file permissions before proceeding on the second method.
Pictorial Guide:
http://i43.tinypic.com/4ida3n.jpg
Create or Edit a post by clicking Posts › Add New or Posts › Edit.
If you are editing a post, select which post you wish to add a thumbnail in.
Upload an image and copy its full URL (external images will NOT work).
Under the Custom Fields meta box, create a new custom field with the Key thumb.
Under the Value field, paste the full URL of the image you have just uploaded.
Save the page and you are done.