The lifeline's usage is similar to that of "Plus One." A friend of the contestant is sitting in the audience next to their "Plus One," and when the contestant needs help, the friend will step onto the stage and try to help them. They will stay on the stage until the contestant either answers the question or walks away.
The lifeline is given to contestants at the beginning of the game, but it can only be used after "Plus One" has been used. This, as well as the "Flip" lifeline during special occasions in the UK, are the only lifelines whose availability depends on that of another lifeline as opposed to how far the contestant has gone in the game.