Any way to paint an object directly into the scene?

I'm a newbie. I have a question about "can we paint an object such as a "Plant" or "Detail object" into a scene directly like a tree or grass? for example, is some kind of dust or detail grass that I need to put it one by one and it feels like this is not the right way to do it, because it very slow to get the job done.

Thank you.

 

It matters very much what you are talking about.

In this case, it sounds like you're talking about adding terrain details (trees and grass) to a 3D scene. If so, yes, you can paint those. See the manual here and here.

But if you're actually talking about something in a 2D game, or for some reason can't use terrains, please be more specific.