What's the difference between 1! and 2! continuous futures?

We have continuous futures on TradingView, for instance, ES1! and ES2! The only difference between these two futures is the additional contracts listed in the ES2!. In other words, 1! has the current contract in front, while the 2! has the next contract in front. 

For example, from December 2018 to March 2019 the main contract for the ES1! Continuous is the March contract ESH2019, the most popular and actively traded. The ES2! continuous shows the next, June contract ESM2019 for the same time period.