The ETIAS travel authorisation will be a mandatory pre-condition for entry to the Schengen States. It will be checked together with the travel documents by the border guards when crossing the EU border.
Is ETIAS a Schengen visa?
Is ETIAS a Visa? No. The ETIAS authorisation is not a visa. Nationals of visa liberalisation countries will continue to travel to the EU without a visa but will simply be required to obtain a travel authorisation via ETIAS prior to their travel.