When new Nodes are created, this global option defines if Nodes should be displayed with a preview thumbnail or without. The preview can, however, be hidden or displayed anytime at Node level.
Here you can define if a grid should be displayed in the Node Editor. The Nodes can then snap to the grid.
Here you can define if you want to define globally if the Navigator should be visible in the Node Editor. This can, however, be switched temporarily in the Node Editor (menu: View/Show Navigator).
If a Node produces errors or has been fed with invalid data types, it will be framed in red (look for error messages in the info area that can give you more information). This red frame can be hidden if you disable the Error option.
Connections are by default displayed using a swung wire (Bezier option). If you want this to be linear simple select the Linear option.