Question on selling options (covered call)

I am new to options
I was thinking to compose my portfolio with large cap low volatily stocks and to sell call options to get the premium.
I was just wondering how it works practically when you sell a call since I haven't done before. This question can sound stupid and naive but still I would like to know

when you sell a call option do you get the premium immediately from the broker or do they need to wait somebody to buy the call first. Can the call finish unsold?

Thanks for the answers

Selling a call is just like selling anything, e.g. a futures contract... If you're filled, you receive the premium.

Martinghoul said:

Selling a call is just like selling anything, e.g. a futures contract... If you're filled, you receive the premium.

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So, may it go unsold?

esculapius1975 said:

So, may it go unsold?

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Well, I don't know quite what you mean by that... Let's say the mkt in spooz is 1210/1211 and you're 1220 offered. Unless at some point there's a 1220 bid, you won't be filled.