Apple removed the complexity of sharing Wi-Fi passwords with other iDevices. When one device is already connected to the network, it will attempt to share the Wi-Fi password with any new iDevice attempting to connect.
In this example my iPhone is connected to the Wi-Fi network, but the iPad is not. By entering
Settings -> Wi-Fi on the iPad and selecting the appropriate network:
The iPhone automatically displays a message asking to share the Wi-Fi password:
Share Password button is pressed, the iPad automatically connects and the iPhone displays a message letting the user know the password is shared successfully: