Here are the instructions Doug McKay posted to the Roots-L mailing list, 
reproduced here with his permission:

From:    "Douglas B. McKay" <dmckay@XMISSION.COM>
Subject: ROOTS-L infobase at http://www.folio.com

I have updated the ROOTS-L archive infobase which has been mentioned here
over the past few days.  It now contains the full text of the archives up
through the last archive file (24 Jun 1995).  There are more than 85,000
messages in the archive comprising nearly 140 MB of original text.  The
infobase file itself is 109 MB (due to Folio's underhead technology).  As
the weekly archives continue to grow, I plan on keeping the infobase up to
date as well.

To use the infobase, point your Web browser at the following URL:

   http://www.folio.com/folio.pgi/roots-l_archive?

Include the '?' or you won't get what you want.  If you set a bookmark for
this location in your browser, it will be easier to come back to in the
future.  The file may change locations over the next few weeks as we rework
our home page, but the above URL should always work.

When you link to this URL, you will see the "Title Page" of the infobase
(anyone have a better graphic?) with a little information about the infobase
(like when it was last updated, etc.)  There is a limited amount of online
help available at this point, but clicking on the "Help" icon on the title
page will give you what's currently available.  The different items on the
"Toolbelt" are briefly explained, etc.  Note that the "Contents" button is
not used at all in the ROOTS-L archive infobase.

Once you've read the title page and are ready to search the infobase, press
the "Query" button and you'll end up with a screen which will allow you to
perform queries on the infobase.

You can simply type in a word ("or" and "and" can be used also) and press
the "Search" button to perform a full text query on the entire infobase.
The results will be shown in the graphical "Results Map" window.  Once you
are satisfied with the number of "hits" your search has generated, press the
"Document" button (at the top of the screen) to view the results of your
search.  Hits will be highlighted with little red triangles.

Since each message is a "record" in the infobase, you may not see any hits
on your screen without scrolling down in your browser.  In order to keep
results displays to a reasonable size, a maximum of 20 records are returned
at a time.  Your browser's window will act as a window to the infobase which
you can scroll up and down.  The "Next" and "Previous" options will scroll
the window 20 records at a time.  The "Next Hit" and "Prev Hit" options will
act somewhat differently depending upon what settings you have in effect at
the time.  Most of the time they will display the next record at the top of
the window.  This way you can scroll through the hits one at a time without
having to scroll your browser's display very much (at least not more than
one message at a time) until you find what you are after.  Note that once
you receive 20 records in you browser, you can also use the "Find" feature
that most browsers include to move quickly through long messages (I've seen
some doosies here :-).

In addition to full text queries, the following fields are available for
searching:

     Date, From, Subject

To Query the infobase using these fields, use the following syntax in the
Query dialog descibed above:

        [Field Date: '6 Mar 1993']
     or
        [Field From: karen isaacson]
     or
        [Field Subject: software review]

Copy these strings into your clipboard (or write them down) then use them
when you select the option Query from the toolbelt.  Obviously, you'll want
to use your own text when performing the searches, but this should serve as
an example.  These examples are also available at the top of the infobase
for future reference.

More advanced searching (such as date ranges and combinations of fields) is
possible, but the above should at least get you started.

I apologize if this all sounds convoluted and unintelligable, I'm not a
documentation writer.  I hope that someone will be able to take these
explanations and rework them into something that the general subscribership
can use.  I'd love to help out in any way I can, and I suppose the best way
may be for you to tell me what you wish to find so that I can attempt to
describe a way to get the desired results.

   ...Doug

   dmckay@xmission.com