Barechu is a Hebrew word that means "blessed are you". When it comes to Jewish prayer, barechu is a special blessing that starts the prayer service by praising and thanking God. It's kind of like saying "hi" to God and getting everyone ready to pray.
During barechu, the prayer leader will usually stand up and say some special words that remind everyone that they are starting a time of prayer and that God is with them. Then everyone else responds by saying "blessed are you, God" back to the prayer leader. It's a way for everyone to join in and express their appreciation for God.
Overall, barechu is an important part of Jewish prayer that helps people get in the right mindset for praying and gives everyone a chance to acknowledge and praise God.