I'm confused how stock options work. Do I need the stock itself to buy them?

I have covered call writing enabled on my online broker account. Does this mean in order for me to buy a call I need to own at least 100 shares of the stock? I know that one call is a contract for 100 stocks. Can I buy one call w/o owning the stock and not exercise it until it goes beyond the strike price and then exercise it? I'm not sure of the differences between naked/covered calls and what I can and cannot do via my broker.

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