Ĉu always forms yes/no questions; if you want your answer to be something other than jes or ne, you need to use a ki- word. :)
it can also be cxu for 'a or b' questions, eg. 'cxu vi trinkas teon aux kafon'
Question words - who, what, when, where, how, how many,
so far duo has introduced "kiel"(who) and now "kiom" (how many), although there might be others - I've not completed all previous lessons
La Esperanton, la Germana, la Angla, la Franca, la Nederlanda (?) en iomete la Welsxa (?)