Here is a short video:
I just fast tracked it, it's old and not really comprehensive, but for start it will do.
Try out Tab Stacking, Split Screen, Session Manager, Quick Commands, Web Panels. Those are just for the start. There are literally 1000x more stuff in that browser, like your own theming (just pick colors and how they will behave), address bar and tab bar positioning, excellent notes integrated into browser, UI scaling, great syncing abilities (you can choose individually what you want to sync, and what not...), every KB shortcut is customizable, etc.
I think it would take 10 pages just to list the DEFAULT possibilities of this browser. And even with no extensions, it's way more powerful then Opera + FF + all extensions possible combined.
And the best part is that EVERY chrome extension works. As do Opera extensions. Give it a week or so, then try using any other browser. It will be like going from a pick up truck to using BMX bike.
Of course, not everyone needs all these features. And everything can be turned on/off, entire point of Vivaldi is complete and full customization. That is the sole reason I love that browser so much. A true successor to Opera browser.