When my PC is on more networks, how does it select the network to connect to the internet?

When my PC is on more networks, how does it select the network to connect
to the internet?

For example: I have 2 ethernet cards, and one wireless, so I'm connected
to 3 networks. But, only the wireless network is connected to the
internet. When I try to access it, it doesn't loads (browsers), so how do
I change the way to connect?