All Saints Day is the day of prayer and celebration of the saints. While most had their own "Feast Day" ie August 24 is the Feast of St Bartholomew, September 8 is celebrated as the St Mary's Day, the Feast Day of St Margaret is November 16, and so on. There is a Saint celebrated every day of the year. List of Feast Days So, I assume, All Saints Day is to catch those Saints that didn't make the annual calendar.
All Souls Day is the day set aside to pray for the souls of those departed. In some cultures it is a day to visit the graves of those family members and loved ones. The graves are cleaned, some times including white washing the tomb stones. Flowers, candles, and other gifts are placed on the graves in memory the departed.
Church services were held for prayer and remembrance of those no longer with us. Traditionally, a list of those in the area who had departed that year was posted on the door of the church.