Is baptism a mandatory step for getting salvation and only through it a person gets the Holy Spirit and the forgiveness of sins? Or is it an important step but it is for declaring that you are a follower of Jesus Christ?
Biblically, there is no question at all about this. In the New Testament, baptism is the point in time when one is "saved." This is clear from passages such as Acts 2:36-38 which make both a cause-effect and a chronological connection between, first repenting, then being baptized, then being forgiven of sins and receiving the Holy Spirit. This is stated as a promise for those present at Pentecost and for all those who are far off–for all who God will call. If you read the writings of the late first and the second century you will discover that there was not the slightest question about the relationship between baptism and forgiveness of sins. Unanimously, it was considered the point in time and the means of salvation (always with the understanding that it is actually the blood of Jesus which is working in baptism, of course). Even the modern-day believers in the baptism-is-just-a-symbol teaching will concede that this is what was practiced and taught in the second century.
Other passages can be used in this connection. John chapter three makes the connection between being born of water and spirit and entering the kingdom of God. Romans 6:2-10 tells us that in baptism we die with Christ and are raised. This is no mere symbol. Anyone who claims that baptism is just a symbolic declaration is not working within a biblical framework. As far as I know, there is not a single passage in the Bible which says that baptism is a declaration that you are a follower of Christ. This is nto a biblical idea, but instead it is an invention of the false baptism-is-only-a-symbol doctrine.