As well as a visual overhaul, Gmail is getting confidential emails, the option to snooze messages, and smart replies, among other new features.
The new-look Gmail is rolling out gradually from today across 1.4 billion or so users, so be patient if it hasn't already appeared in your web browser. To see if it's available for you, click the cog icon in the top right-hand corner of the web interface and look for a "Try the new Gmail" option.
A cleaner, more streamlined interface will be the first change you notice, with a collapsible sidebar on the right where you can display information from Google Calendar, Google Keep, or Google Tasks (now being launched as a standalone app). Attachments appear right underneath conversations too, so you don't have to scroll through the whole thread to get to a photo or an invite.