Minecraft confuses me, can someone explain it all?

I want to play minecraft but it confuses me…
What I don't understand is the whole servers thing, the whole mod thing, and like is it multiplayer like open world where you bump into other people? Or are you alone? What server should I play on?

I was going to watch a YouTube video on it but there are like a million different ones which confused me even more!
There must be someone who can explain it all in layman terms!
Thanks

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