How to create Portal Gun for Portal 2 mod ? Help me guys.

me too bro i need one too

and its not possible without using the custom element (requires knowledge in Java language)

You can use Immersive Portals as an required Mod Dependency for the Portals, because the Mod add the possibility to use a command that creates a Portal just like in Portal 2 :)

Smipa if you want to make a Mod Dependency you need to make a Plugin for MCreator.

Choose one of the Plugins below and extract the Archive and search for the yaml file inside the apis folder to see examples.

Entity Textures Features | ConnectedTexturesMod | Entity Model JSON

And also I recommend to read this page.