I am not surprised you couldn't give an answer as I've found that many Catholics are unable to explain our practices. Either they were never really understood or their meaning simply has been forgotten.
The communion of saints is one of our fundamental beliefs as expressed in the Apostles' Creed that we say at Sunday Masses. What do we mean by the communion of saints? This is a powerful symbol of our connectedness to God and to others, that is, to all living persons and to all those who have gone before us, as well as to the earth itself.
That means that we are never really isolated or separated from the rest of humanity. Just think, we have all those marvellous friends in heaven, even though we never knew them personally. They love and care for us now that they are with God in the same way they exercised their compassion for others during their earthly lives.
Each life is sacred in its creation by God and in God's incarnation into human life to redeem it. The communion of saints speaks of our participation in the holiness of God and of our sharing in the sacredness of life. With God's life and grace in us, together we labour in this world to bring God's love to the rest of humanity.
The Holy Spirit works in and through human cultures everywhere calling all human beings to love God and love others with compassion and justice. Therefore, all are called to be saints and to become holy in their everyday lives of work and struggle, of rest and prayer. Holiness is not the result of our merits, but is God's work in us.
When we understand that those who have died are special friends of God and our friends, it makes more sense to remember them and ask them for help.
Who wouldn't want to help a friend and, after all, they struggled in this earthly life and so can appreciate our needs.
We often use intermediaries to get our needs met as, for example, someone influential will more easily obtain funding for us from a funding agency. We often ask others to pray for us to obtain what we need, health, for example, so too praying to the saints really means that we ask them to intercede for us. We do not expect them to answer our prayers directly for they are not God.
This is what causes confusion for those not familiar with our phrase "praying to the saints."
We know that only God can answer our prayers, but we know in this life God usually answers our prayers through others' work and caring. So why wouldn't God answer our needs through the intercession of those in heaven who helped others with so much love and charity while they were on this earth?
Recently, I was asked, "Why do you pray to the saints?" I pondered the question but realized I had no answer. I asked family members and no one could give me an answer. Would you answer this question for me? Then I can give my friend the answer.