Each client is a router and any intermediary is a router. All of them have tables of routes. This includes your pc, your phone, tablet, everything. a typical client only has one path out. so it would have an extremely basic routing table. in windows you can type route print in your terminal to see it. different systems present the information differently.
0.0.0.0/0 via eno1 is a route. lets say I want to send a packet to 1.1.1.1. It's inside that subnet. It would be sent out of eno1. eno1 may be attached to your router which is attached to your modem. hopefully the routes are set so it goes to your isp who routes it out to the destination.
the subnet 0.0.0.0/0 includes all ipv4 address so anything you send will go out eno1 which is the device like your network card. then the next router looks at the destination and it has it's own routes and it sends it out some network device.
It gets very complicated once you get to where you have many potential paths to the same machine and you have to figure out the best one. This video is very nice to see how one common method works.
View: https://www.youtube.com/watch?v=GazC3A4OQTE