Ah - Unity Lua Scripts, not Unity the 3D Programming environment
You need to think of Unity as a way to parameterise DBP functions. You can pass data (parameters) back and forth and use Lua to manipulate those parameters, create triggers and so on.
For example, you might write a Lua script that passes in trigger zone parameters. In DBP, you'd have a "listener" function that reads in parameters, and acts upon them. e.g
"TRIG~1~120,30,250,90"
In DBP I need a function that knows that a TRIG request requires a trigger box in my scene - named "1", that has x/z coordinates as supplied.
Then I have a second function that sends a request back to Lus when the trigger is hit
"TRIGHIT~1~PLAYER"
This tells me the player (rather than an NPC, vehicle or weapon) has hit the trigger. In response the Lua Script runs a function and reports that a player hitting the trigger is rewarded with more health:
"PLAYER~HEALTH~100"
Finally, DBP processes the increase in health.
Using a messaging system with common keywords and actions allows you / your modder to place objects, zones, actions etc. However it's constrained by the functions you implement in DBP.
Back with your example, you can pass a message that tells the DBP function you have written to create a Sprite using the image you pass and the positions you specify.