The welcome normally includes some kind of icebreaker and games.
The worship time centers on God, who He is and what He has done. We exist to give glory to God, and the worship time initiates that process.
This is always a time of prayer.
The witness time focuses on reaching out to others, which may be planning an evangelistic activity, planning some kind of practical social action ministry, or simply praying in the group for friends and family who need Jesus.
The word time allows God to speak directly to His people through the Scriptures.