Icon Finder Tutorial
First add one of this nodes:
Open Icon Finder, go to Godot's menu Project (1) > Tools (2) > Icon Finder (3) So you can find the icons easily.
You can search (1) icons and change preview size (2), and click on icon you want to use. Button with ❔ opens this online docs.
When you click on icon you want to use it alias will be copy to system clipboard.
Now select Icon node in scene tree.
Look at node Inspector, paste icon alias using
(Ctrl + V
or Right Mouse Button > Paste)
as Icon Name (1) and set it size (2).
Now icons are in your scene: