Trying to understand routes in routes table

Thanks for your response, MiguelUT. I have two public subnets in my VPC. And when I was trying to add the CIDR blocks of the two subnets into the routes table as routes (public subnet CIDR block as Destination and internet gateway as the Target, thinking I need to connect the subnet to IGW to make the internet traffic flow to my subnets) I received the following error, "The destination CIDR block is equal to or more specific than one of this VPC's CIDR blocks. This route can target only an interface or an instance.". This is where I thought that my thinking what routes in a route table are wrong, hence seeking an explanation from the community to correct my misunderstanding on routes in routes table.

UPDATE: In the AWS docs, in this URL, https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Route_Tables.html, for routes table, its says, "You can add a route to your route tables that is more specific than the local route. The destination must match the entire IPv4 or IPv6 CIDR block of a subnet in your VPC. The target must be a NAT gateway, network interface, or Gateway Load Balancer endpoint."

I think this what I took wrong, thinking that I can add subnet CIDR as routes.

If you're trying to route out to the internet then you need to route the 0.0.0.0/0 traffic to the IGW -- that's basically saying any traffic not destined for the subnet (or I guess technically any traffic NOT specifically subject to another route in the table) should go to the internet.