The wifi-ap snap will try to automatically configure the access point after installation with the best options it can automatically determine. You can check with
if the automatic configuration was successful and the access point is already active.
By default the automatic wizard, which runs when the wifi-ap snap is installed, will choose secure enough default password and will enable WPA2-PSK security. You can find the selected password when logged into the system the wifi-ap snap installed on by running the command:
$ sudo wifi-ap.config get wifi.security-passphrase
To enable the WiFi access point manually after the snap was installed and all plugs and slots are connected run the following command:
$ wifi-ap.config set disabled=false
This will mark the access point as being enabled.
Now you have an access point with the SSID Ubuntu spawned up and any WiFi device can connect to it.