Questions regarding to Covered Call

[bbmak]

I am newbie in option trading.
1. Do I need to own the shares before I sell a call contract or write a covered call? If yes, do I have to specific in the contract to tie up the shares? or I just leave the shares in my account, when my contract is called, the shares will automatically sell it to the buyer?
2. If I want to offset the call contract that I sell, I need to buy a call contract at the same strike price?