If you say 'I don't know how to write' then the answer is to start small and work up from there. Flash Fiction (telling a complete story with character(s), a plot, and an ending in less than 250 words) is a good exercise. Flash can be almost any reasonably short length,
but if you can get this style of writing down in 250 words or less on a consistent basis, you are going to become one heck of a better writer. I learned this from a guy named Neil Marr, a good friend of mine who died recently. Before he did, he used to run a writers' site that was very well known. (It closed down in 2009) Anyway...he was a big promoter of flash fiction to improve writing. His theory was if you can get the small stuff polished, the longer stuff will start coming to you naturally. And he was right, I think. I learned a lot from the guy.
A lot of times this is going to be a slice-of-life kind of story.
You need the basics here. A beginning, a plot, characters, a solid ending. If you do it right, you can actually move people with this stuff. Anyone can do 250 words well, right?
So can YOU. Let me post a short example:
Magic Bullet
A man in a silver jumpsuit shimmered into the room like a ghost. He came into focus. “All right, Professor. You know the rules about visiting the past. Lay down the rifle.”
Dr. Andrews continued staring out the window. “I can’t, Mike. I have to do this.”
“You could change everything we know. Put the rifle down or I’ll shoot you myself and take you home in a body bag.”
“Can’t you see the sense of it? I have a perfect shot at the son of a bitch!” Andrews put his eye against the scope again and spotted his target. He saw a man in another window down the street, also holding a rifle. “I’m taking the shot.”
“Put it down.”
“No.”
“Don’t make me do this, Professor. Put down the rifle.”
The crowds on the street below began waving at the motorcade as it approached.
Dr. Andrews hesitated for a moment. Taking his finger off the trigger, he used the rifle as a telescope. “I think he spotted me. He’s looking this way.”
“What?”
“He’s moving away from the window! He’s not going to shoot...”
“Damn you!” The man in the silver jumpsuit grabbed Andrews and shoved him out of the way. The high-powered rifle fell to the floor with a clatter. Snatching up the gun, he took a quick aim at a different target. He knew what he had to do. He centered the ‘x’ on the young man in the Dallas motorcade and squeezed the trigger.
You can DO this. Start really short, work up. The shorter to start, the better. Pick a target for your word count and cut out the deadwood, tighten up the story until you reach that target.
Wow, I just got this overwhelming sense of ultimate power.... 
