There are two thirty minute halfs in NFL football. When there are two minuets left in a half there is a free timeout where the clock stops. Both the first and second halfs have two minute warnings that result in a stoppage of play.
The two minute warning gives each team a free timeout to plan their next move or substitute players. This is an automatic timeout so teams know to expect it. Some teams use the final two minutes of a half to utilize a new game plan that the other team has not seen up to that point. This is a strategy to catch the other side off guard and score points. Some teams are routinely criticized for not having good clock management skills, meaning they don't show any hurry up during the last two minutes.