What is Ice?
Ice is something like ore. One big difference is the volume of ice: Every piece of Ice is 1000 m³ You can find it in Ice belts which are in some systems. There are much less Ice belts than normal asteroid belts.
Ice Types:
Blue Ice (Gallente)
Clear Icicle (Amarr)
Dark Glitter Gelidus
Glacial Mass (Minmatar)
Glare Crust
Krystallos
White Glaze (Caldari)
For what is it needed?
The refined Ice is needed to run POS (Player Owned Stations) A POS uses much Ice per day, so there is always Ice needed for awesome amount of ISK on the EVE market. You can check EVE items relevant and market prices here: http://buyevecheapisk.blogspot.com
What do I need for mining it?
You need at least a Mining Barge (Procurer, Retriever or Covetor) or an Exhumer (Skiff, Mackinaw or Hulk) (Industry V, Mining IV, Astrogeology IV and the skills for the ship class) And you need the Skills Ice Harvesting (Mining IV) and the Ice Harvesters which go for about 2,7m ISK per piece on market. You can find out more in regards of mining here: http://cheapiskeveonline.blogsavy.com/
How can I mine it and how can i optimize my efficiency?
Fit your Ice Harvesters on your Mining Barge/Exhumer. If you can do it, fit Ice Harvester Upgrades. The Mackinaw has a +100% bonus on the yield of Ice Harvesters, but a -25% duration Penalty. The penalty is reduced by 5% fo every Exhumers skill level. So, if you have Exhumer V the Mackinaw has the normal cycle time. The fact that it gets double yield per cycle makes it the most efficient Ice Harvesting ship available. If you can't afford one of those yet, you can get here and buy some ISK for a head start: http://www.mmobux.com/compare/eve/eve-online-isk
But I want to tell you, that Ice Harvesting is it only worth if you have Ice Harvesters II and a Mackinaw with Exhumers V and Ice Harvesting V With that setup you can earn more money with mining Ice than with mining ore. That way you get a real good efficiency and you can earn real much money with mining Ice.