Kintone does have a native plug-in called Conditional Display, which might be perfect for your case.
You can find other native plug-ins here:
Regarding how to install and use plug-ins, please check the following articles:
For your reference, if you would like to customize your Kintone using Javascript, like the one you saw about the Show, Hide, or Restrict Fields tutorial, the following is the best place to start learning about it.
It also explains where and how to attach Javascript files to Kintone apps.