Why do we talk about him so much?
Why do we consider him important?
What did he do?
He saw God, our Heavenly Father, and Jesus Christ.
With that appearance, he found out the truth that they are two different people, not one.
An angel appeared to him and showed him where to find an ancient record of scripture written on gold plates and bound together.
With God's help, he translated that record and discovered it was a record of a prophet and his family who left Jerusalem and came to the Americas. It is a record of the teachings of God, the record of Jesus Christ and his coming to the Americas to visit his "other sheep" mentioned in the bible when Jesus was resurrected.
Joseph restored the truth of the gospel of Jesus Christ that had been lost from the earth since the death of Christ and the apostles.
God restored his authority to perform holy ordinances like baptism, to Joseph Smith.
Joseph received revelations from God that told us that smoking, drinking alcoholic drinks and coffee and tea are bad for us - 150 years before modern science figured it out.
God's temple ordinances were restored through Joseph.
In the end, Joseph gave his life as he was murdered by a mob.
There's more, much more. He was a modern prophet, he received revelation and authority to restore the gospel to the earth.
There is NO other authority on earth given from God. It was lost and had to be restored.
It's true, you can find it too. Look for more at mormon.org