What are they and why are they helpful?
To 'bless' is to bestow favour, and so to 'give a blessing' is to 'bestow God's favour'. Therefore, to bless one another in God's name helps us to know we are cherished and loved by God.
Often 'blessings' are given at the end of a service as a kind of dismissal, but they can be given at any time in the service. As we dedicate ourselves to God to serve him with our whole lives, we continue to be transformed to be more like Jesus in all we say and do. We are then 'sent out' as God's representatives to 'be Jesus' to the world.