A biblical fast can be defined as simply abstaining from food for spiritual purposes. In the Bible, meals and food preparation took a lot more time, and physical and mental energy, than we generally spend on it today. There were no grocery stores and no drive-thrus. Yet, it was encouraged and expected by Jesus that believers would fast (Matt. 6:17-18, Matt. 9:15), taking the time and energy spent for food preparation and consumption and spending it instead on seeking God. For many Christians, fasting in our current culture can mean abstinence from food, as well as from television and other forms of entertainment, and spending the time normally given to those things to instead draw closer to God. What makes this time of fasting rich is using the time to pray, read the Bible, and worship God for fasting. “It was a personal matter between the disciple and his Master, in the light of needs and circumstances.” This is for informational purposes only and is not meant to prescribe any fasting requirement.
There are many other variations of fasting. This is a simple list to give you some ideas. There is an abundance of information available on the internet. We can also point you to resources we know of if you contact the church office. The most important thing about any fast is to follow the leading of the Holy Spirit and fast unto God. We do not want to find ourselves guilty of fasting for the praise of peers, as Jesus warned against in Matthew 6:16-18.
Pray about what/how God would have you fast over these 21 days. Whatever time you normally spend on the activity you set aside, spend that time with the Lord in prayer, Scripture reading, and worship. Connect with others who are also participating and pray together.