How to create triangle mesh?

Hello everyone. I am a beginner in 3D.
How can I make something like this in SketchUp

Check out the Sandbox Tools extension.

Activate the extension via:
Window (menu) > Preferences (dialog) > Extensions (panel)

Turn on it’s toolbar via: View (menu) > Toolbars (dialog)

Search this forum about Sandbox Tools:

Search the Extension Warehouse for other mesh extensions:

… or from the Extension Warehouse window within SketchUp, type “mesh” in the EW search box and press ENTER.

You can have a look at the plugin Artisan (39 USD):