A scaffolder is someone who assembles and/or supervises the assembly of temporary platforms or scaffolding. Scaffolding is mainly associated with building and construction, probably because that's where people see it most. However, scaffolders work in all kinds of situations, from oil rigs to carnivals, where temporary platforms are needed. The work is almost always outdoors, so you must be prepared to work in all kinds of weather conditions. Scaffolding, by its nature, involves heights, sometimes quite considerable ones, so you must also have a good head for heights and be prepared for work with some level of hazard involved. The work can be fairly physically demanding and requires careful planning and precision.
Scaffolding will require you to travel. Depending on the type of work you do, you may occasionally travel long distances or even work under a fly-in, fly-out arrangement. You will probably find it necessary or at least very useful to also have a drivers' licence.
As a scaffolder, you will be responsible for deciding what kind of scaffolding to construct in particular circumstances, which requires a knowledge of different kinds of buildings, building work, and the kinds of load the scaffolding will be bearing. Once this is established, you will then be responsible for the construction of the scaffold, which involves fitting the steel tubes together correctly and placing boards and planks in the right places and with the right kinds of support, as well as safely attaching ladders so that the scaffold is accessible. You will also be responsible for checking the scaffolding to ensure it remains safe once it has been assembled. Finally, you will oversee and assist with the safe deconstruction of the scaffolding, and loading it back onto the vehicle(s).