The key thing is you need some paths to combine, create those using the pen tool or use an existing set of paths. Once you have your open paths and you can only combine open paths with this technique then you can go the node tool and use that to position one of the paths at the end point of the other path.
Go to the node tool and then drag over one of the paths or click the first node in the path and hold down the shift key and then click all the points. Then click the last point and drag that on top of the first or last point of the other path (id you have more than two paths you can repeat this with the others)
Now drag over all the points in both of the paths and then go to the control bar and actions and click the join button (four buttons in the actions) and now you will see only one path in the layers instead of two. If you have more than two then just repeat this with the next path and so on. You will now have a single curve design which can then be manipulated using the node tool or add layer effects etc to the open path. Note that the same steps can be done in Photo as well