The leveleditor can be found in:
It needs to stay in this location since it uses its location to get engine core properties.
Launching the .exe file, will show this window.
The left side shows a empty box, that will be filled with entities as soon as you adds the application folder (path to your project).
To do this GoTo File->Application Directory
Select the correct one and press Choose.
Now list contains entities ready to be added to the level
here is a little gif showing how to add.
Pressing on a entity in Entities List or in the widget, displays its information in the PropertiesView
Next to the entity in the enity list is its name, which can be modified in propertyview
Press Update Enity to save.
File->Save Level/Load Level-><filename>.xml