God has given Christians a great deal of freedom. While he has commanded and forbidden many things, we have freedom in the ways that we conduct much of our lives. He doesn't command a particular mode of worship, what clothes we should wear to church, or what color we should make the walls. All of this falls under Christian freedom.
St. Paul describes a situation where some are judging other Christians for practices that fall under Christian freedom. It seems that some Jewish Christians were still eating kosher and holding to the old holidays. Some Christians looked down on those still doing the old ways as if they were weak in the faith. Paul writes that Christians are free to practice certain habits or disciplines if they want to.
It's important to remember that Christian freedom doesn't mean that we can do whatever we want. God still commands that we hear his word, receive his sacraments, and follow his will. All our decisions about what we do should drive toward the best way to serve that aim.