Ice breaker basically plow through sea ice. The thick stuff they ride up on and break using the weight of the ship. They have a rounded hull and a sloping prow that allows this, but also makes them notorious for wallowing in heavy seas.
Some icebreakers have propellers in the bow that break up ice and propel forward. They are powered by electric motors that are strung to diesel generators in the rear. Same as many rear propellers are turned by electric motors (don’t quiz me on this)