At the current time, Splatoon 2 is the only game that's compatible with Nintendo Switch Online, and it will allow players to voice chat with friends, invite people to online matches, create teams, and access SplatNet 2.
SplatNet 2, designed specifically for Splatoon 2, offers up online play statistics like match results, stages, and rankings. It also lets users invite friends with Splatoon 2 to Private Battles, League Battles, and Splatfest battles across social media.
While Nintendo Switch Online is limited to Splatoon 2 right now, future games will have built in support, with Nintendo Switch Online serving as the hub for most interactive features like voice chat. When using voice chat, Nintendo says it works in different ways based on the game that's being played. Users can either chat with everyone in the room or split voice chat into teams.
The app's functionality and the Splatoon 2 online play will be available for free until the full Nintendo Switch Online service launches in 2018. Following the launch of Nintendo Switch Online, most games with online gameplay will require an ongoing subscription. Nintendo Switch Online will cost $19.99 per year or $3.99 per month with a monthly subscription.
A persistent internet connection is required to use the app, as is a Nintendo Switch console, and a Nintendo Account. Users must be at least 13 years old to download and use the app, and it won't work until Splatoon 2 is released on July 21. For now, expect to see a login error when attempting to sign in with a Nintendo account.
Nintendo Switch Online can be downloaded from the App Store for free. [Direct Link]