The alter is up and running in Vecna's Tomb, you merely have to walk up to it and say Vecna Lives to make an offering to Vecna.  Currently the alter accepts only Vecna Coins (Iron, Copper, Bronze, Ice, Electrum, Platinum).
If you have a Skull of Vecna that has some of the slots filled from his soul you will find Vecna a little more incline to see your offering favorably.  All offerings are gathered towards being given a reward, the better the coins, some related skills that favor the dead and luck will all help you along the path.  At some point you will get something, always just depends on if you keep at it.  Once you receive something, it all resets and you start over. 

Now since everyone wants to know, what are the rewards... 
For starters this is the only way to get bonus set slots, you will learn about this in the very near future.  Needless to say, if you wish to group up your gear into a specific bonus set?  Use those Glyphs?  See how Vecna's Essence can be useful?  This is the first step towards that door. 
You will also find this as a source for Battleworn Vecna and Kas gear, in addition to the related Mystery Chests.
Finding coins and craftables...Pretty much everything in the tome at this point has a chance to drop something.  In almost all cases it is craftable related though which if you find the Coin Press I am sure you will figure out the rest on your own.  You will need to craft a specific number of iron coins before you can start crafting copper, then copper to get to bronze, etc.  But know this, offering Platinum coins to the alter is without a doubt far better then any coin under it and the same logic applies down for the other coins as well. 

These coins will also have addition value in some other systems we have coming as well.

Every drop chance, reward in the tomb, spawning, timers, etc etc etc is going to change.  These are just numbers I have in place until I see things unfold.  If anyone was around for Dungeon of Sin they will tell you I spend 6 months down there tweaking until I liked it and did what I had visioned.  Even the mobs will no double get some recoding done.  Relax and enjoy.  This is just the start of some rather crazy rewards I have in mind for this place that fit the theme of the tomb.

Important Safety Tips and Information

1.  Some mobs do require different approaches to fighting, might take spells or even specific energy types.2.  The higher level the mob the higher chance of special loot... and dangers.3.  The alter is at the start of Vecna's Tomb

Is there any way to combine those coin press charges? Dragging on each other does nothing.

Yes.. that is coming the middle of next month but didn't want to jump the gun so to speak.  No need for such a thing if no one is minting coins yet.   First I am making sure basic code is working as expected and then we move forward releasing other new stuff that relates.