how to use line tool like video for adobe animate

Hi mate,

It's called Motion Guide. Look it up. There would be many examples how one can set it up.

What the author of the video shows there is applicable in some very rare cases, but extremely impractical in character animation.

There are better methods available to you now - Layer Parenting and Smart Magnet Rigs.

Motion guides are very good when you control a complex trajectory of one object, but motion guiding body parts of a rig during character animation is absurd, except for in some rare situation when you need slow motion between two keyframes. And that, as he shows, will need to be in a duplicated symbol as it pollutes the character timeline by doubling the number of layers.

Hope this helps!