You can just randomly generate an address, or use the initial one that gets generated by default, and use that to receive bitcoins immediately. As long as you have the private key for it (well, your Bitcoin client takes care of that, storing your private key in your wallet file) you can spend any bitcoins that get paid to that address.
thank you again i got it finally
when i have good amount of coins in my wallet will use one of good security method
my both question is clear now only now i wanted to know how i make deal like we do in paypal if buyer want to buy anything i usually deal in Dollar and Euro but how i calculate how much bitcoin = $ or Euro and what is the main difference between them !! any guide or your reply will help me alot thanks once again !