Dear Lior,
#Plugins Dir
To get plugins to work, you must download them and extract them to this folder structure
YourProject/Plugins
So the folder “Plugins” is in the same directory as your .uasset.
Please note the spelling must be exact!
#In the Editor
Then you go in the editor
Windows->Plugins
and check off which ones you want to activate
#Writing Your Own
If you are writing your own plugin,
it gets compiled along with the rest of your source code
#Plugin C++ Source Example
I have a plugin with an additional editor mode and 35 additional Blueprint nodes here
I have included my entire source code in the download