Writing by hand or by computer is your decision. I've known many writers who write by hand and later write by computer. I've never known anyone who writes by computer and switches to writing by hand, though.
Because you're writing only text, you can get a 2GB USB drive. You can fit a few books that are already written on that.
A story, whether it's a novel, short story, or screenplay, is started with some of the following:
1. Premise. This is when you ask, "What would happen if?" Anything can get you started with it. The author of "Lord of the Rings" started his when he wrote about a hole in the ground on a piece of paper. He had no clue what it meant, he simply wrote it. Then he started asking "what would happen if..." something lived in it? Then it grew into "The Hobbit" and "Lord of the Rings". Brainstorm, read the news, and start asking what if questions to develop the premise of your story.
2. Setting. You can set your story anywhere, on Mars, in the past on Earth, in the future on a starship, anywhere. Even thinking about the setting can help you to develop the premise.
3. Multiple Characters. Almost all stories contain multiple characters to play off of the values of the others. Start thinking about characters and what they want and this will also help you to develop your story. Ask lots of "what would happen if?"
4. Inciting Incident. This is where you story begins that turns your story's world upside-down and forces your character to set it straight. Then your character will begin a quest to reach an object of desire. Thinking about an inciting incident can also be your premise: "What would happen if a shark ate someone and the partially-eaten body ends up on the beach?" Jaws.
These points should help you to get started. Once you understand these concepts, you can then research the story structure so that you can actually finish it because once you hit the middle, you'll find it becomes work.
Write a story wiki:
http://www.storyentertainment.com/ow