To break the ice means to get people who have not met before to feel relaxed and to start talking to each other.

Examples:

She said, "Here's a game that's guaranteed to break the ice at parties".

The room was silent, so he told a joke to break the ice.

Sometimes it's very difficult to break the ice with our new students because they are so shy.

Take note

To put something on ice. If you put something on ice you delay it.

Example:

We decided to put the project on ice for a while and concentrate on doing other things.