The Altar works like a mixture of Vanilla Minecraft's Enchantment Table and Furnace. You can add Ambrosium Shards as a fuel to the altar (just add the ambrosium shards to your hotkey bar and click with the right mouse button on the altar), the maxium ammount you can add is 16, and then you can add several other items right after, which will then transform into other items.
An example is: You can add 4 Ambrosium Shards and 1 Gravitite ore to the Altar, and it will result in one Enchanted Gravitite, which is used to craft the Gravitite tier of items
It also acts like an Anvil as it can repair armor, tools and accessories but as of now it is bugged.
Yes, I forgot to say that aswell. Thanks for posting that :D
I have sent a bug report to Brandon (Kingbdogz) and I'm waiting maybe an answer. There were many bugs in there, including this one. I hope they get fixed soon