What are the curling positions?

lead

second

vice

skip

The lead throws the first two stones of an end.

The second throws the 3rd and 4th stones.

The vice skip (or "third") throws the 5th and 6th stones.

The skip throws the last two stones.

In addition, the skip acts as the team "captain" and strategist. The skip stands in the house (scoring) area and signals/tells the other players what shot should be thrown, and holds his broom where the shooter should aim.

While the skip is shooting his/her stones, the vice holds the broom in the house, hence the term "vice skip."