I recently had the awesome experience of having my oldest cousin leave on her mission!
Now, what a missionary for the Church does is leave home for 2yrs for boys, and 18 months for girls. They live there life totally for other people-- inviting them to come to Christ, and serving them.
In 2012, Pres. Monson changed the ages that men and women could leave for their mission: boys could now leave at 18 (before it was 19), and girls could leave when they were 19 (previously 21).
After this, there has been a HUGE increase in missionaries in the field. Here is a news article from the Church about it, and about the lives of some missionaries in New York, NY.
I personally am preparing for my mission. You need to pay for it yourself, so I am saving up my money. I'm also doing my best to live a life that would make my Heavenly Father proud of me, and that sets a good example to others.
The message of the missionaries (and of the church) is that through Christ you cam make it to Heaven, and be with Heavenly Father again. Even if you're imperfect, Christ has performed the Atonement for us, and we can change.
I'm going to end by sharing this poem (again):
After All We Can Do
By Robbie Pierce I had been in that hole for a very long time-
In the dark and the damp, in the cold and the slime.
The shaft was above me; I saw it quite clear,
But there's no way I ever could reach it from here.
I could not remember the world way up there,
So I lost every hope and gave in to despair.
I knew nothing but darkness, the floor, and the wall.
Then from off in the distance I heard someone call:
"Get up! Get ready! There's nothing the matter!
Take rocks and take sticks and build up a fine ladder!"
This was a thought that had not crossed my mind,
I started to stack all the stones I could find.
When I ran out of stones, then old sticks were my goal,
For some way or another I'd climb from that hole.
I soon had a ladder that stood very tall,
And I thought, I'll soon leave this place once and for all!
I climbed up my ladder, a difficult chore,
For from lifting those boulders, my shoulders were sore.
I climbed up the ladder, but soon had to stop,
For my ladder stopped short, some ten feet from the top.
I went back down my ladder and felt all around,
But there were no more boulders, nor sticks to be found.
I sat down in the darkness and started to cry.
I'd done all I could do, and I gave my best try.
But in spite of my work, in this hole I must die.
And all I could do was to sit and think, Why?
Was my ladder too short? Was my hole much too deep?
Then from way up on high came a voice: "Do not weep."
And then faith, hope, and love entered into my chest
As the voice calmly told me that I'd done my best.
He said, You have worked hard, and your labor's been rough,
But the ladder you've built is at last tall enough.
So do not despair there is reason to hope,
Just climb up my ladder; I'll throw down my rope.
I climbed up my ladder, then climbed up the cored.
When I got to the top of it, there stood the Lord.
I've never been happier; my struggle was done.
I blinked in the brightness that came from the Son.
I fell to the ground as His feet I did kiss.
I cried, "Lord, can I ever repay Thee for this?"
He looked all about. There were holes in the ground.
They had people inside, and were seen all around.
There were thousands of holes that were damp dark and deep.
Then the Lord looked at me, and He said: "Feed my sheep,"
And He went on his way to save other lost souls.
So I got right to work, calling down to the holes,
"Get up! Get ready! There is nothing the matter!
Take rocks, and take sticks, and build up a fine ladder!"
It now was my calling to spread the good word,
The most glorious message that man ever heard:
That there's one who is coming to save one and all,
And we need to be ready when He gives the call.
He'll pull us all out of the holes that we're in
And save all our souls from cold, death, and from sin.
So do not lose faith; there is reason to hope:
Just climb up your ladder; He'll throw down His rope
