so basically, there are devices that

1. repeats traffic it gets, ie it broadcasts to everyone connected to it, and also used for extending ranges. ie the repeaters and hubs. and range extenders for wireless.
2. devices that routes traffic to where it needs to go, ie only the specific device connected gets the traffic. ie switches, and access points for wireless.
3. devices that connect networks together, ie a local area network to a wide area network or two different wide area networks. ie routers
4. devices that converts one signal format to another signal format, ie analog to digital or digital to analog or coax to wifi, or whatever. . ie modems and transceivers

so basically using the postal service analogy. your post office is a router. all your mail goes through your post office. mail intended for an address not serviced by your post office is delivered to another post office (and that post office figures out where it needs to go). the mail delivery man is like the switch. they connect to your post office (router) and deliver the mail to your door. now a days, hubs/repeaters are typically not used anymore because that's like everyone in your post office delivery area getting everyone's else's mail as well, but you just throw away mail not intended for you.