Yes, Catholics pray to Mary and the saints but we do *not* worship them. When a Catholic prays to a saint they are asking them to pray for them. It's the same kind of thing as me asking you to pray for me.
Yes, Catholics pray for the dead. Mainly out of the belief in Purgatory which mostly comes from the Books of Machabees which I'm 99% sure you don't acknowledge (If unsure, just ask your father) so I won't waste your time quoting it. Jesus speaks of forgiveness of sins in "the world to come" (Matt. 12:32) which Catholics believe to be Purgatory. "Every man's work shall be made manifest [on the Lord's day]: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is. If any man's work abide which he hath built thereupon, he shall receive a reward. If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire." (I Cor. 3: 13-15) With these words Catholics believe that the soul of man will ultimately be saved but he will suffer a time in Purgatory to make up for his sins. Not really "make up" for his sins but free him from the temporal punishment of sin.
Jesus also prayed for the dead. He prayed to the Father before he raised Lazarus from the dead (John 11:41). Jarius also begged Jesus to raise his daughter (Luke 8:41). In 2 Timothy 1:18 Saint Paul prays for Onesiphorus who died. That is three example of people praying for the dead in the Bible.