Now on Tap is the one of the best feature of Android Marshmallow version. This feature work with the press of your finger, and your phone will predict what you wanted to do with information from screen. I know it's very technical but here is the full video of how this feature works on your phone and tablet.
I found this ad from Google's YouTube Channel and it's very informative and clear about how this feature works.
I hope after watching above video/AD now you understand the use/concept of Google Now On Tap feature. Know in brief at below.
Now On Tap Feature/USE :
- Basically this feature saves you to copying and pasting info from one tab/Window to another.
- This feature will also reduce tedious switching back and forth between apps.
- We got this feature before an half year. And now we are getting an video ad of this feature. One thing I have noticed in video that End of the video they refers to the feature as "Only on Android M".