Presets list is binded with node type. Meaning that principled BSDF node has different preset menu than Glass BSDF.
Refresh List = Sometimes can happen that presets are not showing in the menu. Pressing this button helps.
Delete selected = delete selected preset from menu
Save into library = Saves current node tree into selected node. Only saves those nodes that has connection into your selected node.
Load from library = Load preset into your selected node.