The film is attached to the backing paper at one end only, this is the end that feeds through the camera first. So when the whole roll is exposed and you load it on to a spiral, the backing paper just curls away and the end of the film is free.

You just have to feed the film on to the spiral. With Jobo spirals this is a lot easier IMO because they are designed to let you grip the edge of the film as it is loaded. The more film on the spiral, the more there is to grip and the easier loading becomes.

My advice would be to sacrifice a cheap roll of film and have a go in daylight so you can see exactly what is happening. Don't forget that an unexposed roll will have the film taped to the backing paper, it might be best to run it through the Holga first to simulate it being exposed.