This is a typical view for a part file
Additional items may be added/removed as needed
The origin is the (0,0,0) location which is the basis of all models. It is the intersection between the three Default Workplanes
It appears Blue in the Part Environment while it appears Red in the Sketch Environment
You may type text into the filter box to see a filtered list of tree items
This comes in handy in Assemblies
If you see the arrow next to a tree item, you may LMB the ⮞/⮟ (Arrow) to expand/collapse it
You may press SHIFT+C to collapse all items
You may RMB an item on the tree and click the Eye icon to temporarily hide/show an item
NOTE: This is different than the Eye on the Heads Up Toolbar which overrides "Little Eyes" in the Design Tree
By default when in a Command, the tree will automatically switch over to the properties view. When looking at the properties, you may have to select tree items. In these cases, you'll have to select items from the Secondary Tree which should appear in the graphics area to the right of the Design Tree
If you wanted to see the origin, which icon would you click to View the Origin