Argentina, despite failing to impress against either Bosnia or Iran, are through to the second round, and barring a loss to Nigeria today they're through in first. Nigeria are the other side that control their own destiny, but having failed to look entirely convincing themselves in their first two matches, advancement is far from certain. At present, they have four points and a +1 goal differential, with Iran behind them on a point and -1 goal differential. The short answer, then, is that if Nigeria can win or draw they're through. Lose and it gets complicated.
That's because if Nigeria lose, their goal differential drops at least by one. And if Iran win, theirs rises by at least one. The next tie-breaker is goals scored, where Nigeria have a goal and Iran none, but if Iran win—and they looked dangerous at times against Argentina in their last outing—that edge could disappear. The next tie-breaker is head to head, and the two sides drew. After that it goes to a coin flip. Nigeria control their own destiny today, but they face the group favourites in their match and if Iran can get a goal against Bosnia, Group F might well go to a coin flip to determine who advances.