When Christians pray to the saints, they ask for them to intercede and pray for the individual to God. Similarly to when we ask family members to pray for the trials that we are facing.
This practice replicates the urging found in 1st Timothy, where he asks for the supplications, prayers, petitions, and thanksgiving to be offered for everyone. In the book of Revelations, we learn about the Apostle John's vision of heaven. In this vision, he saw the saints in heaven holding our prayers in their hands and letting those prayers rise to God.
It takes time and practice to finish a rosary. Similar to building a new muscle. The 15-20 minutes of an entire rosary is often too much for the new user. Yet, new users can benefit from praying smaller sections of a solo rosary, such as the opening prayers and the first decade. After a while, you will feel ready to pray a full rosary and eventually join others in simultaneous community prayers.