The basic premise of splatoon inknation intro is that you land in an airport in inkopolis and you get asked to pull out your id you would customise your inkling or octoling and flooling(when you unlock them) as you go along eventually after your done you can proceed and take a taxi to inktopia where you get the tutorial in general

to go into story mode you go down an alleyway where you get squidnapped and take a series of challenges to escape with the help of the squid beak splatoon from nesu and marina hacking in and making things easier if you choose to

I’m still working on the story for story mode inknation I might call it the squidnapping