Although you don't mention the book's title, I hope you won't be misled by what it seems to be teaching. Nowhere in the Bible does God promise to give us anything we want, if we'll just believe strongly enough. What we want may not be God's will for us and God's will is always best.
Be on your guard also against any teaching that sounds good on the surface but leaves Jesus out of the picture. Why do some authors omit Him? I don't know the reason in this case, but often it's because they deny that our most basic problem is our sin, and believe instead that we have the power within ourselves to solve our problems. This appeals to our pride, and we don't like to admit that it's wrong.
But sin cuts us off from God, and it also weakens us and makes us unable to change our lives. Only Christ can take away our sins and change our hearts and He will, as we humble ourselves and turn our lives over to Him. The Bible says, "Therefore, if anyone is in Christ, he is a new creation; the old has gone, the new has come!" (2 Corinthians 5:17).
Don't be misled by those who claim you can have spiritual power apart from God or Christ. Instead, by faith turn to Jesus Christ and commit your life to Him. Then begin following Him, and not those who urge you to take a different path.