Lightly oil the interior of the steamer. Transfer the couscous to the steamer, taking care not to compress or pack the couscous. Place the steamer on top of the base of the couscoussier. Presumably you'll be stewing some meat and vegetables in the bottom, but you could also steam the couscous over salted water.
If any steam escapes from the joint where the steamer and base meet, you'll want to seal the joint. You can do this in one of several ways:
* wrap and tie a long piece of damp cloth over the joint, or
* tightly wrap a long piece of kitchen plastic film around the joint, or
* wrap and drape a long piece of kitchen plastic film onto the rim of the couscoussier, and then place the basket on top (this is my preferred method)
Once you see steam rise from the couscous, allow the couscous to steam for a full 15 minutes.