Paul took the 5th chapter to address a specific person that has apparently been have a physical relationship with either his mother or step mother.
In verses 2-5 Paul admonishes the church at Corinth to put this person out of the church. It appears that Paul is basically telling the leadership of the church that they can not allow one person to damage the message of the gospel.
Verses 6-8 Paul makes reference to leaven. Leaven of course is similar to yeast which once allowed to activate will grow bread to twice or perhaps three times its original size. Perhaps Paul is warning the church to stop the such actions before they fester and grow into something that it should not.
In verse 9-11 the church is told to not only put this person out of the church but he continued to say not to even keep company with such a person.
One of the potentially confusing parts of this chapter is that we are told all the way through the chapter to avoid sinful people. However, in the last two verses Paul explains the rules of judgement.
Basically, Paul has told the people in the church to NOT judge anyone without first judging themselves.