Most commentators will point out that of all the pieces of the armor, the "sword of the Spirit" is the only offensive weapon mentioned. Of course, in Bible days, it was the sword that was the equivalent to our modern day police officer's gun. The sword was available to the soldier to use if necessary to defend himself, defend someone else, or show an intimidating weapon that would cause the enemy to either flee or surrender.
Thinking about the "word of God" as our weapon there are a few things that might be helpful. First, its not just having a sword that will aid a Christian in battle. Its being familiar with your weapon that is important. Get a Bible you can understand and then open it! Seek help from older Christians who can show you the basic layout of the Bible, the various books, the chapter and verse divisions. Get to know how to find a reference in the Bible. Ask for help in finding out where to look in the Bible for helpful insights about God, salvation, Christian living, etc.
Second, the Word of God is meant to give the believer the means to oppose the enemy when temptation comes or when trials and difficulties arise. God's Word in a believer's heart can keep the believer from sin - Psalm 119:11 KJV, "Thy Word have I hid in my heart that I might not sin against Thee." God's Word helps keep a Christian strong against the enemy. It also gives the believer the promises of God to believe to be encouraged during trials. Verses like Philippians 4:13 show a believer that their strength comes from Christ or Philippians 4:6,7 that shows a Christian why they don't need to worry about anything if they would learn to pray about everything! There are many other ways in which the Word of God ministers to a believe helping them to face the enemy.
Third, the Word of God is God's message of salvation for the world. It is therefore the believer's weapon of opportunity to share this Good News with everyone! We are told to preach the Gospel and make disciples for Christ. It is the Word of God that touches the heart. 1 Peter 1:23 NKJV, "having been born again, not of corruptible seed but incorruptible, through the word of God which lives and abides forever!" Share this glorious message with others.
Fourth, and perhaps most important, the Word of God is meant to be read every day and meditated on all throughout a believer's life. Psalm 1:2 NKJV, "But his delight is in the law of the Lord, and in His law he meditates day and night." This "sword of the Spirit" is never to be out of a believer's life! The Christian needs to have God's Word available in his hand and in his heart to fight the good fight of faith.
One final thought from Psalm 119:97 NKJV - "Oh, how I love Your law!..." Love the Word of God and treasure it highly in your life.