See VOP structs for more information on using structs in VOPs.
To create a struct, wire the values you want as the members into the node’s multi-input.
In the parameter editor, you can name the members. This will make wiring and debugging easier. If the name is blank, Houdini uses the name of the wire. In some cases this will be what you want anyway (for example, if the input is from a Parameter node, the default name is the parameter name).
You can reorder the inputs in the parameter editor.