Your grandmother gave you the greatest gift she possibly could -- the Word of God. The Bible isn't just another book; it isn't even one of the greatest books that has ever been written. The Bible is God's Word, given to us so we can come to know Him, love Him and serve Him. As the psalmist said, "Your word is a lamp to my feet and a light for my path" (Psalm 119:105).
And I want to assure you that the Bible isn't just for preachers! God wants to speak to you -- and He will, if you will make the effort to listen to His Word and apply it to your life. The Bible says, "Do not merely listen to the word. ... Do what it says" (James 1:22).
How can you do this? First, get a Bible you can understand. Perhaps your grandmother gave you an older translation that she has loved over the years -- but if you find it difficult to understand, a newer translation will be of more use to you. You don't want to offend your grandmother, of course, but your Christian bookstore can suggest a modern translation you can use in addition to the one she gave you.
Then set aside time each day to read your Bible -- even if it's only a few minutes at first. I suggest you begin with one of the Gospels (such as John). There you will discover the greatest news of all -- that God loves you, and Christ came to save you.