An Archetype Entity is an entity that has its properties defined in the entity archetype library in the Database view. If you change a property of an entity in the Archetype library it is reflected in all archetypes of that type that are placed in all levels. This is good for consistency. You can make sure that a barrel for example has the same weight in all levels or a certain AI type has the same sight range all over the game.
In this example I'm going to show you how to create an Archetype Entity. You'll be able to reuse the red alert light in any level.
Creating a new library
First, open the Database View ( View => Open View Pane => Database View ). Then click on 'Add Library' and type in a name of your choice, press OK to create it.
Creating a new Item
Now click on 'Add New Item' and select the Entity Class Light ( Lights/Light )
Naming the item
Type in a name for the group, in which the item is going to show up. Groups are Subcategories of the Library. Logically, you should put all your Lights into a 'Lights'-Group. Then type in a name for the actual item, in this case 'Red_Alert_light'
Tweaking the parameters
Now tweak the light however you want. You can just drag it into your level to see what it looks like. I've set the Light Style to 1, increased the DiffuseMultiplier, SpecularMultiplier HDRDynamic and the color.
Now you can drag as many Archtypes as you want into any level. You just have to load your library and you're done.