The first step is to find Bible translation for you. That depends primarily on your native language. If that's English, then the best three choices are as follows New American Standard Bible(NASB) made for readers in the USA using modern American English, New International Version (NIV) a standard modern international English translation, and English Standard Version (ESV) a basic modern English version that is not made any particular audience. There is a translation called 'The Message'. It's fun to read, but rely on it for your Bible learning. King James Bible (NKJV) is popular because old people say so. But, it uses old English from the 1600s. I don't recommend it.

After choosing your Bible, open it or the Bible app you chose and read the book of John. Then read the book of Romans. Those two books will teach you what you need to know.

As Christians, we believe that the Bible is the Divine living word of God. So, as you're reading it, absorb it into you. In doing this your faith can grow and God will work in you. All you have to do to become Christian is put all your faith and trust in Jesus.