Example:
Start with $2 million cash.
Buy 50,000 shares of MOVIEX at $10 per share = $500,000 invested. You have $1.5 million in cash left, but you also have to pay commission of 1% (= $5K), so your cash is now $1.495M and net worth is $1,995,000
MOVIEX goes up in price by $1. Your net worth is now $550,000 in MOVIEX and $1,495,000 in cash. Net worth = $2,045,000.
You sell MOVIEX. Net worth is now $1,495,000 in cash you have, plus $550,000 in cash from selling the stock, less the $5,500 you have to pay in commission on the sale. Net worth = $2,039,500.
Short is what you do when you expect a moviestock's price to go down, and cover is how you "sell" a short. You can find out more about this in the What is HSX?, Glossary and FAQ links at the bottom of the page.
Since you're a new player, you should try to identify the stocks that will change most in price - buy if you think the price will go up and short if the price would go down. You can get some good predictions of when stocks will move by checking the Movies board for news. Good news, like a big budget movie going into production, or getting a new star = buy. Bad news, like a movie being cancelled = short. Just remember to get out of the investment when the movement has run its course.