It will be available as part of the Nintendo Switch Online phone app coming alongside the game on July 21st.
Per Nintendo's earlier announcements about the Switch's online service, this is still an early version of the app, with a final, more fully featured version set to release with the full launch of the Switch's online service sometime in 2018.
That all takes place via the Nintendo Switch Online app, which will allow players to invite each other to Private Battles, Salmon Run, Splatfest Battles, and League Battles as well as offer communication with players who opt in to voice chat. The new service, which is known as SplatNet 2, will provide game stats and let players use voice chat and send multiplayer invites for the game.
The goal of the app, per Nintendo's website, is to enhance the online experience for compatible Switch games. Sometimes you just don't want to shoot ink around a skate park for a couple hours while you wait for other maps to cycle through.
If single-player is more your thing, the single-player mode also sees you going on an adventure to find Callie of the Squid Sisters.
Splatoon 2 is getting an online demo. Make sure you show off your freshest records to your friends via social media!
Annie is planning to open an online store called "SplatNet Shop"!
The store is still getting ready for its grand opening at the moment, but should be available in a future update so check back soon!