"What was the practice of casting lots?"
The practice of casting lots is mentioned 70 times in the Old Testament and seven times in the New Testament. In spite of the many references to casting lots in the Old Testament, nothing is known about the actual lots themselves. They could have been sticks of various lengths, flat stones like coins, or some kind of dice; but their exact nature is unknown. The closest modern practice to casting lots is likely flipping a coin.
The practice of casting lots occurs most often in connection with the division of the land under Joshua (Joshua chapter 14-21), a procedure that God instructed the Israelites on several times in the Book of Numbers (Numbers 26:55; 33:54; 34:13; 36:2). God allowed the Israelites to cast lots in order to determine His will for a given situation (Joshua 18:6-10; 1 Chronicles 24:5,31). Various offices and functions in the Temple were also determined by lot (1 Chronicles 24:5,31; 25:8-9; 26:13-14). The sailors on Jonah's ship (Jonah 1:7) also cast lots to determine who had brought God's wrath upon their ship. The 11 Apostles cast lots to determine who would replace Judas (Acts 1:26). Casting lots eventually became a game people played and made wagers on. This is seen in how the Roman soldiers cast lots for Jesus’ garments (Matthew 27:35).
The New Testament nowhere instructs Christian to use a method similar to casting lots to help with decision making. In Acts chapter 1, when the apostles cast lots to determine who would replace Judas, this likely was not God’s desire for the apostles. Jesus had repeatedly told the apostles to wait for the Holy Spirit (Acts 1:4-5), who would instruct them and give them wisdom. That is how we are to discern God’s will today – not by casting lots, rolling dice, or flipping a coin.