It is a central routing function.
It connects different az together and connects the vpc to an internet gateway.
You can have up to 200 route tables per vpc.
You can use up to 50 route entries per route table.
Each subnet must be associated with only one Route table at any given time.
If you don't associate any subnet with the route table, that subnet is associated with the default vpc route table.
You can also edit the main route table if you need, but you cannot delete the main route table.
However, you can make a custom route table manually and assign it as a main route table and then you can delete the former main route table because that is no longer a main route table.
You can associate multiple subnets with the same route table.

An internet gateway is a virtual router that connects a vpc to the internet.
Default vpc is already attached with an internet gateway.
If you create a new vpc you must attach the internet gateway to access the internet.
Ensure your subnets route table points to the internet gateway.
It performs NAT between your public and private ipv4 address.
it supports both ipv4 and ipv6.

AWS VPC: Implied router, Route table and Internet gateway.