What are "works"?

A lot of the so-called "Christian Denominations" believe Ephesians 2:8-9 means that in order to become saved all a sinner has to do is "believe" and do nothing else. But this is not what the holy scriptures teach.

Firstly it's important to know that all of Ephesians is written to Christians, people that have already obeyed the gospel of Jesus Christ like those that obeyed Acts 2:38 (see the beginning of this in Acts 19:1-7):

Ephesians chapter 2 is explaining how the Jews and the Gentiles become the same, by the Spirit of God, the Holy Ghost.