Jesus had freed a man from demons, and the man who had experienced the miracle the Bible says he begged Jesus to let him go with Him. 

I believe that when we experience miracles in our lives we should allow that miracle to impact the world and that is how we can truly go with Jesus. I believe that is what Jesus was telling this man. 

Go Tell: 

Tell it to your family
Tell it to your neighbors
Tell it to anyone who will listen

Tell them what?

What God has done for you
How Good God is in your life
What it means to you to follow 

In Habakkuk 2:2 it says that we should take the message, we should make it plain, and then we should write it on the walls so people can see it.

Your experience with Christ, your testimony about Christ's work in your life is the best message people could hear.

3 Points:

Take the message:
Make it plain (simple, understandable)
Declare it to anyone who will listen

38 The man who had been freed from the demons begged to go with him. But Jesus sent him home, saying, 39 “No, go back to your family, and tell them everything God has done for you.” So he went all through the town proclaiming the great things Jesus had done for him. ~Luke 8:38