There are two different types - rusks and biscuits. Rusks are generally in stick, cylindrical form - they're hard and NOT meant to be eaten - more for them to just grind their teeth on to soothe the teething pain. Biscuits or wafers are thin - can be eaten like normal biscuits. However, whichever it is, they should NOT be given to LO when it breaks apart. Most biscuit packs would also give a warning behind that it should not be consumed if broken because (while unlikely) it might be stuck in their throats without proper chewing.
Chewed on and then thrown away at end of the day.