From LSWiki

The only real info that can be found about the glomerates is in a random load book called Nihilgenesis, by Marcus Lucretius Maro.

The book is in latin so you'll need decent skill in it (close to 40) and literacy to be able to read it.

The book itself is vague but gives a lot of hints regarding the use of your powers as a glomerate.

Joining

To join you'll need to first find a non-descript silver ring set with a harlequin opal.

You'll need a free point in INT for Ektilaturgy.

You will also need to read the book Nihilgenesis.

You'll need to be able to either "hold" or "wear" the ring, so exceptionally large characters may have issues joining.

If you are too large you may be able to have the ring resized by Celebrimbor or Puzzled by an aligned.

Once you have the ring, say 'EX NIHIL SUM' in latin while holding or wearing it.

The Ring

  This is an exquisitely-crafted ring composed out of a single smooth piece of
   silver.  It reflects and absorbs the light oddly, sometimes casting back glints
   of dazzling color, sometimes gleaming with faint and ghostly hues.  There is a
   small harlequin opal set into the inside of the band.  The gem seems to separate
   two written phrases: EX NIHIL SUM and IN NIHIL SUM.  You estimate its value at
   about six thousand nine hundred gold.
      It is in perfect condition.
      It is intermediate in size, and definitely too small for you.  It looks about
  a twentieth of a dimin across and a fifth of a dimin around.  It weighs about
  a hundredth of a dekan.

Void

Once you have joined, you can establish a connection with the void by concentrating. The command is "concentrate on stilling my mind." Note that you must rest for a minute or two before attempting this, and you will have to do it every time you die (as death severs your connection to the void).

Nihilsphaera

Once you have joined, you will need to craft a nihilsphaera, or orb of nothingess. Find a gargantuan spider, and cut out its spinneret (you may need sufficient anatomy and insect lore for this step, or have an expert cut the spinneret from any spider's opisthosoma and give it to you, whereupon you can identify it with a lens). Once done, perform the command "cast nihilsphaera creo with spinneret". You will create a nihilsphaera, a sort of cosmic black hole that fuels your powers as a Glomerate.

Powers

Comprimere

Accelerates the compression process inherent in one's nihilsphaera, with the intention of siphoning off as much void energy as possible for one's own use.  The steps for casting this spell -- of which the first is 
optional -- are prepare one's nihilsphaera for compression and fill oneself with a portion of the resultant Void.