I am beginner in crypto-currencies, i just created my account in cryptsy and can make buy/sell orders but how do i accept orders from others(i.e open orders(all buy/sell orders)) i can view the list of all buy/sell orders but don't know how to accept those orders?
You cannot accept or reject an order. When you place a sell order (for clarity's sake assume 1 BTC for 100 dollar) and there is no-one with a buy order above $100/BTC you end up in the list of buy orders. When someone thinks "hmm, that is a nice price to pay for a bitcoin" he can create a buy order for 1 BTC (or less) for $100/BTC. Cryptsy looks then if there is a sell order for that price (or lower) and his order will be filled, and you get your money. So if you leave an order open while you go away, it can be filled without you noticing it.
If you want more clarity about the filling of orders, you can look at my answer here.
edit: so if you want to close the deal immediately, buy (or sell) at a rate that there is a seller who sells at that rate. Otherwise the market can go up, and your bid will be missed out.