The Bible-based websites listed below present the clearest explanations on these subjects that I've found:

www.iiw.org is the official website for the "It Is Written" ministry, which is one of the longest-running and most watched TV religious programs in the world, and now is conducting Evangelism Seminars worldwide, in a tremendous effort to reach "every nation, and kindred, and tongue and people" with God's final warning to the world just before Jesus returns.

www.BibleInfo.com is a good site for answers to many questions being raised today by Bible Students.

www.Sabbath-Day.net is a very clear and Biblical explanation of why many believe that proper Sabbath observance will play a prominent part in the testing at the end of time.

www.666mark-of-the-beast.org is a very thought-provoking explanation of Revelation, the Book of the final days of our world as we know it, the Book given to prepare us for our Lord's return to earth.