Not all features will be available at launch. Those immediately available include smart replies (similar to the Calendar.), the option to and a new tool panel on the right side of Gmail's interface for easy access to Tasks (also revamped) and
The process to get the new look and features will depend on the type of Google account you have. If you don't have the option to enable the new feature, whether you're a G Suite admin or a regular user, keep checking back. Google is rolling out access today in waves.
Regular Gmail users
You can enable the new look and features by clicking on the Settings cog in the top-right corner, then selecting Try the new Mail option.
G Suite users
If you have a Gmail account that you use for work or school, then the account administrator will need to enable the new Gmail through the Early Adopter Program.
The administrator will need to use the Google Admin console and opt in to the new Gmail.