“Discernment — the ability to think biblically about all areas of life — is indispensable to an uncompromising life. It is incumbent upon the Christian to seize upon the discernment that God has provided for in His precious truth! Without it, Christians are at risk of being “tossed here and there by waves, and carried about by every wind of doctrine” (Ephesians 4:14).”
Pastor John MacArthur gives this excellent definition in an article on his website, Grace to You. This ministry is committed to spreading the Word through careful and responsible teaching of the Bible by a very gifted teacher. On the website you will find links to a large variety of free articles, sermons, and answers to tough questions. I suggest finding a sermon series on a theme or book of the Bible that interests you. Use the search engine to explore by topic or Scripture. Then choose a regular time to listen while you commute, exercise, or work around the house. Trust me, cleaning your bathroom will feel way more enjoyable if you can soak up some Ephesians in the process!
You can check out this article and other great resources at Grace to You: http://www.gty.org/resources/questions/QA138/What-is-biblical-discernment-and-why-is-it-important