Icebergs are huge chunks of ice that break off from the ice collected around land, or from glaciers that reach the sea. They float, but most of them is underwater and you can't see it, which has coined the phrase "tip of the iceberg" meaning that you can only see a small part of something and the problem is actually a lot bigger than it seems.
Ice cream is a dessert made from frozen milk or cream. Icecream is usually flavoured with sugar, vanilla, fruit or chocolate. Icecream is made by freezing the milk or cream slowly and stirring it frequently so it stays smooth. If you don't stir it, it will be full of crunchy ice crystals and will not be as nice. Icecream is sometimes served in a cone.