As a Christian, here's how I (personally) see it (and this is my long answer, so bare with me):

God is all good. He created everything to be good. His desire was for everything He created to live in peace and fulfill the assignments they were created for. And because there was peace and fulfillment in everything He created, all of creation loved God, understood God, and worshiped Him.

However, after a while of seeing everything operate in it's God-given assignment, God decided to open up "choice" to everyone. First to the angels and then to humans. He wanted us to have the choice of whether or not we would do what He created us for or to do whatever we desired.

God didn't want His creation to love Him because He made us love Him. He wanted us to love Him because we chose to. Because we saw all our options (good and bad) and chose to love Him above everything sin - a life without God - had to offer.

There was no such thing as "choice" before God created it and gave us the will to use it. Without "choice" the angels served God and worshiped Him, and humans did the same, always feeling peaceful and fulfilled, never feeling empty or confused about life, existence, or God.

Now, since God is all good and His purpose for us is all good, then that makes the opposite of God and the opposite of His purpose all evil. (I hope I didn't lose anyone.)

Now, Lucifer (Satan, the angel who we consider all evil) was the first living creature to use "choice" to leave God and make his own purpose for himself. Why? Because Lucifer wanted God's creations to worship him instead of God.

So, when God created humans, Lucifer deceived us by making us think we could live a better life without God. So when Eve chose to do what she wanted (bite the fruit that God told her not to touch) she brought all evil into God's good world.

Anything sad, tragic, bad, evil, and not good are all on Earth as a result of sin, of choosing to be without God, who is all good.

That's why God is all good, because He only wants good for us. Anything not good is a result of sin.

That's why when something good happens, we thank God. But when bad things happen, it is because WE (human beings) chose to live by our own evil desires. Bad things NEVER happen because God made them happen. Bad things happen as a result of sin.

I know this is a lot. I wrote it rather quickly, so excuse me for not editing. I'm rather busy today. But I had to take a stab at the original question. I hope this helps.