A route table contains a set of rules, called routes, that specifies how packets should be routed in a virtual network. Route tables are associated to subnets, and each packet leaving a subnet is handled based on the associated route table. Each route table can be associated to multiple subnets, but a subnet can only be associated to a single route table.
Packets are matched to routes using the destination. This can be an IP address, a virtual network gateway, a virtual appliance, or the internet. If a matching route can't be found, then the packet is dropped. By default, every subnet in a virtual network is associated with a set of built-in routes. These allow traffic between virtual machines in a virtual network; virtual machines and an address space as defined by a local network gateway; and virtual machines and the internet.
There are no additional charges for creating route tables in Microsoft Azure.