And boy, does he need those prayers. They are called prayers of intercession. Very simply, it means "praying for others."
More specifically, "Intercession is prayer that pleads with God for your needs and the needs of others. But it is also much more than that. Intercession involves taking hold of God's will and refusing to let go until His will comes to pass. Intercession is warfare -- the key to God's battle plan for our lives. But the battleground is not of this earth. The Bible says, 'We are not fighting against humans. We are fighting against forces and authorities and against rulers of darkness and spiritual powers in the heavens above' (Eph. 6:12)." (http://www.cbn.com/spirituallife/cbnteachingsheets/keys-intercession.aspx)
This is what the people of Bedford Falls are doing for George Bailey. They are pleading for God's help in order to save George from his struggle and despair.
In response to those prayers, we see a debate occur in Heaven. We see Joseph and Franklin (See previous entry about the letter F) discussing the wisdom of sending Clarence, the hapless, wingless, simple-minded second-class angel.
It takes some work, but Clarence succeeds and George returns home. The prayers of intercession, as well as George's own prayers, have been answered.