Few Simple Netowrk Questions

1. Routers are used to connected mutiply network , right? How about switch? Can it also connect mutiply network just by using the UPLINK connections?
So what are the difference in the usage of switch and router? (I know that they are base on layer2 and layer3, in which router has path determination..but so what? )

2. Can I said router is a gateway? Why do we need a gateway?

3. ppl todays mostly using routers to share Broadband to the Internet? Why can’t a hub or switch in doing so?
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I am now learning CCNA semeaster 1, but just got those silly questions. It would be great if you can help me. Thx a lot!