"Many people picture a missionary as a middle-aged man who leaves his job in America to evangelize and plant churches in Africa. But that is a simplistic view. Today, African Christians reach out to Muslims in the Middle East. College students spend their summer teaching English in Asia. A family in America befriends and witnesses to international students. A truck driver responds to an international disaster, meeting both physical and spiritual needs. All these are missionaries.
Although missionaries cannot be stereotyped, they each have a call. God calls them to set aside personal ambitions in order to be witnesses of the Gospel. Like Isaiah, a missionary gladly responds, "Here am I. Send me!" (Isaiah 6:8b). Often God sends a missionary to a particular people group as Paul was sent to the unreached Gentiles and Peter to the Jews (Galatians 2:8). Although technically a Christian missionary is one specifically called by God and sent out by the local church, every Christian has a mission to make disciples. " (from GotQuestions.org)
I whole heartily believe that our Lord Jesus Christ ask all Christian believers to make Him known, in action, in words and by example. We have all been gifted in different ways so its going to look different so don't compare the work the Lord has put before you to others work.
A simple way I answer this question is "we work amongst Ecuadorians and students of different nationalities our desire is to let them know that there is another way to live life and to give them the opportunity and help them see by example that Jesus Christ Listens, Jesus Christ Saves, Jesus Christ is God, Jesus forgives and His Word is real and relevant to our life." I carefully chose the word opportunity because we don't shove His Word down people throats, we don't stand out in the street yelling "that your going to hell."
Our Missions Pastor shared his broad definition of missions "Engagement with God's mission to help all nations enjoy His glory and forgiveness through Jesus. This would make all Christ-followers missionaries... of course, some do this full-time vocationally."
I hope this gives you a basic idea of what is a Christian Missionary.
My response in a picture form below: The world, His Salvation, His people.