First, remember that God, not us, save others. Second remember that Hell is not a place but an absence of God. You cannot “go” to hell, you can only put yourself in a place far from God.
My friend explained it worked like this.
You hear of someone giving out free $100 bills…after some sort of trial. You pass the obsticle course for yourself and get the $100. Then you decide you want to do it for a friend. You do it and put the money in an envelope and put it in your friend’s hands.
The friend can choose to open the envelope and help themselves with their finances. They may give the envelope to the bank and hope for the best without looking. They may throw out the envelope.
This is similiar to the spiritual life. We are all connected through the body of Christ. God gives graces to us to get us through difficult situation. These graces are also given for non-trials such as mass, the rosary and many other prayers. When we will we can store up these graces for others.
In some cases the grace can be used immediatly. The reciepient (as with the money) can choose to immediatly use the graces to see that God is helping them through a hard time with extra love and support. The recipient can be willfully or unwillfully ignorant and accept it (as with the bank) and God himself can ply the heart with intense prayers. The recipiant can be hostile (throwing out the money) and God will store the graces for when the person is willing to recieve them.