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 1:1-2 King James Version 1 Paul, an apostle of Jesus Christ by the will of God, to the saints which are at Ephesus, and to the faithful in Christ Jesus: 2 Grace be to you, and peace, from God our Father, and from the Lord Jesus Christ.
Ephesians chapter 2 is explaining how the Jews and the Gentiles become the same, by the Spirit of God, the Holy Ghost.
Ephesians 2:8 King James Version 8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
2 Timothy 1:6-7 King James Version Therefore I put thee in remembrance that thou stir up the gift of God, which is in thee by the putting on of my hands. 7 For God hath not given us the spirit of fear; but of power, and of love, and of a sound mind.
With these two verses we see that the "gift of God" is the Holy Ghost. With that information when we go back to Ephesians 2:8, it is revealed that the "grace" spoken about here is the Holy Ghost that has been given to the saints. Let's take a closer look:
Romans 4:16 King James Version 16 Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all,
Ephesians 2:9 King James Version 9 Not of works, lest any man should boast.
Many confuse this verse and say that "works" means actions or anything a person can do. But this is not what the holy scriptures teach:
Romans 3:27-28 King James Version 27 Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith. 28 Therefore we conclude that a man is justified by faith without the deeds of the law.
Here we see that "works" are revealed as "deeds of the law". The "works" talked about in Ephesians 2:9 are the deeds of the law, which were the ordinances that the Jews kept along with the Ten Commandments.
Hebrews 9:10 King James Version 10 Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation.
They had over 600 ordinances they kept, also referred to as the law of righteousness:
Romans 9:31 King James Version 31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
Titus 3:5 King James Version 5 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;
Belief is important and is the first step in becoming a Christian (Acts 2:37). The next steps are to repent, be baptized in the name of Jesus Christ and receive the gift of the Holy ghost (Acts 2:38):
Acts 2:37-38 King James Version 37 Now when they heard this, they were pricked in their heart, and said unto Peter and to the rest of the apostles, Men and brethren, what shall we do? 38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
This is what the holy scriptures teach.
See "How to be Saved" to know how to become a Christian.