This is from the UOX3 Message Board by Dupre the Fighter:

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Posted by Dupre the Fighter on October 12, 1998 at 14:47:39:

First, you need to set up the three paths at the bottom
of the screen. 
staidx0.mul (staldx0.mul is wrong)
statics0.mul
uox3.wsc

Initially, when you start up worldforge, those three
bars will be red. When you've entered the correct
path, they will turn green. The nice part of version
2.1 is that it now remembers the paths that you entered
in so that you dont have to re enter them everytime
you start up worldforge.
Once you have the path set up, you then need to get
the statics info. Just press the GetStaticsIndex button
and it will take a few seconds to process the information.
Once its done, all of the other buttons will now be
highlighted (that is, they will work now).

To edit the statics0.mul file (ie. to move static items
from the statics0.mul file to your .wsc file where you
can edit/delete them), first get the coordinates of
the location you want to edit. I'll use an example here
to avoid any confusion. Im going to edit a location
in Lord Britishs castle (x1385 y1635 z30). 

**NOTE: Always back up both your .wsc file, statics0.mul
file and staidx0.mul files**

Now, you need to enter the x and y coordinates in
worldforge. To do so, you need to divide both the
x and y value (in this case x1385 and y1635) by 8.
x1385 divided by 8 = 173.125 (173 - you have to use
whole numbers here)
y1635 divided by 8 = 204.375 (204)

Once you enter those numbers, hit the GetStaticBlocks
buttons and a list of tiles will be listed on the left.

Now, enter those two numbers in worldforge and then
hit the Melt button. Worldforge will now begin to
move the selected static blocks from the statics0.mul
file to your .wsc file. You will also notice, once
done, that it will cover an area several tiles from
those coordinates. You now can edit/change/move/delete
those static items since they are now in your wsc file.
Once you are done, all you need to do is hit the Freeze
button and all of those items will be moved back into
your statics0.mul file. Also to note here, when you
moved your static objects into your .wsc file, worldforge
has given all of them a Type number of 255.
In order to move items to and from your wsc file, they
must have a type 255 value (worldforge looks for this
and will only move those items, and no others).

To move items you created from your .wsc file to your
statics0.mul file, all you need to do is to create
your item and then set its type to 255 (/settype 255).
When you hit the Freeze button, all items with a type
255 will be moved from your wsc file to your statics0.mul file. 

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Thanks to Dupre!