As one of Vuo's developers, I work on Vuo's engine (the thing that makes compositions run), work on nodes, and write documentation. You'll see me on the forums answering people's questions about Vuo.
I enjoy using Vuo to make live music visuals. My hope for Vuo is that it will grow into a community of people of diverse backgrounds and identities making lots of different artistic, useful, unique, goofy, beautiful, crafty, wonderful compositions.
Estoy practicando para ser competente en español. Si publicas en el foro en español, trataré de responder en la misma manera.
Wait, what? I must have mixed up your composition with something else. You have provided 3 vertices. On my computer, your composition does output a triangle. This is on Vuo 1.2.8 with, I believe, the latest version of the Parabox node set installed.
To use the Parabox Make Mesh with Values node, you need to understand the basics of meshes. I would recommend spending some time reading or watching videos to understand the background.
To answer your immediate questions: For the node to output a non-empty mesh, it needs at least 3 vertices (Positions and Elements) as inputs. Elements are indices into Positions (0 refers to the 1st item in Positions, 1 refers to the 2nd item in Positions, etc.) that have to do with how the mesh is assembled.