As for markers in the marker library, you can use Marker Symbol Editor to create a marker, or you can import markers from other existing resources, or even you can save the object in the map as a marker. The supported object to be converted into markers include point, line, polygon and text. (2D objects only)
Select an object which you want to convert to a marker, and right click and choose Export as Point. A Marker Symbol Editor pops up. You can change the marker style and shape. For detailed operations, please see Edit Marker Symbol.
After you complete the marker style, you click on OK. The new marker is saved into the current workspace. When you make a map next time, you can select this new marker from the Marker library and apply it into the point layer.