Who is Joseph Smith?

Actor who plays Joseph Smith

Well, the Simple answer to that Question is that Joseph Smith was a Servant of The Lord Jesus Christ. Namely, he was God's chosen Prophet for this day in the Time (About 1830 - 1844 AD) that he lived. Therefore, like Moses, Abraham, or Noah, Joseph Smith was, at his time, the divinely chosen leader of Heavenly Father's Children, given the task to instruct God's Children as to the will of God in our Day, that we might have the opportunity to continually progress and one day live with Him again.

Establishing some Background

Sound presumptuous? Maybe; But let me take you to some scriptures.
Genesis Chapter 7 Verse 7 reads: "And Noah went in, and his sons, and his wife, and his sons' wives with him, into the ark, because of the waters of the flood"
A prophet of about 600 years of age, with only 7 followers.

Even without a computer, He's still pretty awesome.

Exodus Chapter 14 Verse 12 reads: "Is not this the Word that we did tell thee in Egypt, saying, Let us alone, that we may serve the Egyptians? For it had been better for us to serve the Egyptians, than that we should die in the wilderness
A Prophet sent to deliver God's Children from bondage, and God's Children would that he had never come.

Lamentations Chapter 1 Verse 1 reads: "How Doth the city sit solitary, that was full of people! How is she become as a widow! She that was great among the nations, and princess among the provinces, how is she become tributary!"
...And so a nation who was given a prophet to guide them out of the conquering hands of the Babylonians lies in heaps of ash because they would not listen to the Prophet of their day.

And Finally, St. Matthew Chapter 26 Verse 66-68 Reads: "What Think ye? They answered and said, His is guilty of death. Then did they spit in his face, and buffeted him; and others smote him with the pals of their hands, Saying, prophesy unto us, thou Christ, Who is he that smote thee?"
For though the Son of God himself would appear to lead the Children of God, still Jesus Christ is rejected with the least and greatest of the prophets.

You see? It is as Jesus Taught, "A prophet is not without honour, but in his own country, and among his own kin, and in his own house" Mark 6:4. Prophets of old have been rejected because, much like today, the Children of God for some reason believed that God eventually stops loving us enough to send us guidance.  But I am here to testify that God the Father has not stopped loving us. He is the same Yesterday, Today, and Tomorrow, for that is what he taught of himself. Therefore, now, as in times of old, God has sent a prophet to the Earth to make known His Will.

What did Joseph Smith Do?

Lots of Things, but since we don't have forever, and you don't want to read a novel, here are just a couple.
Under the Direction of Heavenly Father, and after Receiving from explicit permission to act in His name (called the Priesthood) Joseph Smith preached the Word of God to the children of men, translated the Book of Mormon from Ancient records inscribed on golden plates and buried in the ground, Re-established or restored the Church of Jesus Christ in the same way and with the same organization as it had been organized by Jesus Christ Himself while He was on the Earth, lead the members of that Church out of harms way to a place where they could safely worship God, and Prophesied and received revelation for our day so that we could know for a surety how to live that way God intends for us to Live. Joseph lived a good life endeavoring to continually live the way he was being taught by God. Like Moses, Noah, or even Christ, Joseph came to this world in a time where the 100% pure word of God did not Exist, so he was tasked with rebuilding bridge from us here on Earth to Our Heavenly Father.

Why do we need a prophet? Isn't The Bible Enough?

Can you ask the bible what a computer is? Can you ask the Bible What the proper way to use the internet is? If you asked Moses whether or not we should smoke cigars, what would he say? 
The problem is, though God does not change, we do. We are constantly learning, creating, changing, and moving about. We need living Scriptures. Noah's revelation to build an Ark did not instruct Moses as to how to rescue the Israelites from Egypt, and Moses' revelation did not tell Jeremiah to preach repentance to Jerusalem lest they be destroyed. They were living scripture in their day, and now, out of love, Heavenly Father has sent Living scriptures to ensure that we know the way back to Him. We still have the agency to choose, but at least Heavenly Father has done His part.

How Can I know This is True?

My suggestion is to read the bible. First see if you can pull out some of the things that Christ did while on the Earth pertaining to organizing a Church. Then, compare that to the way The Church of Jesus Christ of Latter-Day Saints is organized. Above all, pray to the one person you know who can't lie. Ask Him if this is His work. When you get your answer, remember, our doors are always open. We Love You. I love You. God the Father and Jesus Christ Love you. Seek for their word, and you shall find.
May the Lord Bless us in our search for Him. In the Name of Jesus Christ, Amen.