Acts 16:1 - 3

"He came to Derbe and then to Lystra, where a disciple named Timothy lived, whose mother was a Jewess and a believer, but whose father was a Greek. The brothers at Lystra and Iconium spoke well of him. Paul wanted to take him along on the journey, so he circumcised him because of the Jews who lived in that area, for they all knew that his father was a Greek." NIV translation

Paul went to Lystra where he met Timothy. As Timothy had a Jewish mother and a Gentile father, he would have been considered an outsider. He was a respected believer in the area and Paul wanted to take him along on his journey. Paul circumcised Timothy even though the leaders in Jerusalem had said that it was not necessary (see chapter 15). 

This shows us the kind of faith that Timothy had as he willingly suffered the pain of circumcision so that he would not be a stumbling block to the Jews of that area.

Acts 16:4 & 5

"As they traveled from town to town, they delivered the decisions reached by the apostles and elders in Jerusalem for the people to obey. So the churches were strengthened in the faith and grew daily in numbers." NIV translation

So, Paul and Timothy traveled around to the towns and helped to answer the questions of the young believers. This served to strengthen them in their walk as Christians and is what Jesus meant when he said to "go and make disciples". We also see that, as they grew in their faith, the number of believers grew as well. That is because disciples share their faith with those around them.