Etriers (or Aiders, and more properly étriers) are tape ladders used in aid climbing, generally in conjunction with a fifi hook apiece. It is sensible to have them different colours as this makes tangles easier to sort out.
Fifi Hooks are used to hook the etrier into whatever you intend to dangle it from. Generally you'll need two.
Big Wall Etriers are durable and as comfortable as possible to stand in.
Alpine Etriers are very light and designed for occasional aid use on alpine routes.
Adjustable Etriers are a lightweight alternative to Big Wall Etriers and can also be used as Alpine Etriers.