You can right-click any parameter in the Parameters Panel and Export it. This adds it to the Library Panel, and allows it to be used as the value of other parameters. You cannot export two parameters with the same name.
You can delete an exported parameter. To do this right click on the exported parameter (or the Value Node) and select "Unexport". It will delete the current selected exported Value Node but it will not affect to any parameter that was connected to the exported Value Node.
Exported canvases cannot be deleted for the time being.
Exported Value Nodes are visible in the Library Panel only for the current edited canvas. So if you export the canvas parameter and then double click in the Canvas Dialog you will open the canvas in edit mode in another window. You can export a parameter while editing that canvas, and then the exported parameter will be visible only in the canvas scope. It will allow have same exported name for several Value Nodes in different canvases.
You can also rename an exported parameter. Just make right click on the exported parameter (or the exported Value Node. It will not affect to the connected parameters that will remain connected to that renamed ValueNode.
You can convert any exported Value Node using the Convert right click menu. But there is a difference: converting a connected parameter will disconnect from its exported Value Node. But if you convert a Value Node all the connected parameter will follow the converted Value Node.