The LDS considers the Book of Mormon to be the words of Gods prophets (parts of the twelve tribes who had been seperated) who lived long ago on the American continent in the new wolrd. They testified of Christ and His coming in Palestine, just as the Bible is God's word in the Old Word to His prophets there and is His witness for Christ.
As such, the Book of Mormon is considered to go hand in hand with the BIble in testifying of Christ. That is its purpose. "In the mouths of two or more witnesses."
That is how the LDS faith views the Book of Mormon, believing that both are scripture.
Not looking for contention, just explaining the faith.