The Bible says,

"And the Lord added to the church daily such as should be saved." - Acts 2:47 KJV

How were souls added to the church?

Peter preached the gospel on the Day of Pentecost. He preached that Jesus died for our sins, that He was buried, and that on the third day He rose again.

"Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do?" - Acts 2:37 KJV

Peter then told the people what to do.

"Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost." - Acts 2:38 KJV

"For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call. And with many other words did he testify and exhort, saying, Save yourselves from this untoward generation." - Acts 2:39-40 KJV

"Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls." - Acts 2:41 KJV

That day, those that were water and Spirit baptized were added to the church. (John 3:5). They were water baptized in Jesus name for the remission of sins (Acts 4:12), and were baptized with God’s Spirit speaking in other tongues as the Spirit gave them utterance (Acts 2:4). This is how souls are added to the church. (Acts 10:44-48, Acts 15:3, Acts 19:1-7).

"And they continued stedfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers." - Acts 2:42 KJV

This is the church that Jesus founded, and this is how it began. And this is how souls today are added to the church.

"And the Lord added to the church daily such as should be saved." - Acts 2:47 KJV