Your pastor is only echoing Jesus' words to His disciples, telling them to be His witnesses to the whole world. In His final words to them He declared, "But you will receive power when the Holy Spirit comes on you; and you will be my witnesses ... to the ends of the earth" (Acts 1:8).
How can you become a better witness for Christ? First, be sure you understand what Jesus Christ has done for you. He willingly left the glory of heaven and took on human flesh -- suffering scorn and rejection, and finally enduring the agony of the cross. Why did He do this? He did it because He loves us -- and once you understand just how deep His love for you is, your life will never be the same, and you'll also want to tell others about His love.
Then pray regularly for people you know who don't know Christ. Ask God to work in their hearts and give them a hunger for Himself -- something only He can do. Then ask Him to help you be friends to them, showing them by your life that Jesus Christ makes a difference to you. Pray too that God will give you the right words to say when He gives you the opportunity.
In addition, learn from others how to communicate the Gospel. We're all different; we don't all have the same personality or the same gifts. But God can still use us -- and He will, as we trust Him and seek His help to share Christ with others.