I am a Christian, and no specification needs to bee done. One is either a Christian or they aren't. Many claim to be Christians but don't understand what it really means to be one. Christians do, however, vary beliefs on certain theological issues, but that will not change rather they are or are not Christians.
I believe in Christianity because of what I consider to be overwhelming evidence that supports it. The biggest evidence of all is myself. Who I am. The way that I have changed because of my belief in Christ and my acceptance of Him being my Lord and Savior.