I answered this on the youtube post.

in bootstrap file, there are many folder and file. I don’t know which file is use for what job. Please, tell me details.

What bootstrap have you downloaded?

i download this bootstrap. https://github.com/twbs/bootstrap/archive/v4.0.0-alpha.2.zip

can i make animated type menu using bootstrap v4. http://kybarg.github.io/bootstrap-dropdown-hover/index.html . this link contain some animated type menu using v3. have any way to convert it in v4.

You could do manual conversion but I would recommend using the Bootstrap version recommended for the plugin you are integrating .