Google 2 Step Verification adds an extra layer of security on top of a Google account thus preventing the usage of the propagation of the real password on simultaneous devices.
The Google 2 Step Verification is a way of protecting the Google Account's password access.
Enabling it, assigns a trusted computer/laptop/handset or device (in generic terms) to be the sole access for that said account.
For the other devices to be able to access it, a one-time password must be generated on the trusted device, in order to use it on another device, instead of the real Google account password.
In that way the real password is shielded (and only on the trusted device) and makes it harder to break.