I see that some Muslims have prayer beads. What do we use them for? Is it similar to Christians using a Rosary? Is this a mandatory practice for all Muslims to use and have?
Its called Misbaha or Tasbih. Some people use them to keep count for Dhikr. For example if they wish to say "Alhamdulilah" a specific number of times, they will say it while pushing the beads, when they reach the end they will know they have said it equal to the number of the beads. It is not mandatory.