1. Was ist der Unterschied zwischen ;-)
2. it's the situation you're using it: währen: old fashioned way of dauern; anhalten: most time for an activity or mentality, dauern: you can always use it
3. Gewerkschaft is a union of labourers and employees, union is mostly used for political or non-person constructs
4. Watte is any smooth material mostly from cellulose or polyester, Baumwolle is cotton
5. Darbietung is an artistic show, Präsentation is equal to presentation in English
6. impact in the sense that something crashes on s.th. else: a comet can einschlagen but also an idea can "einschlagen wie ein Komet" meaning that an unexpected idea occurse with an overwhelming effect

What ThorusCrusius said, and adding to 4. Watte is the material of a cotton ball (Wattebausch in German), Baumwolle is the fabric of a cotton dress.

3: To draw a sloppy English analogy, Ge-werk-schaft = work-ship. So die Gewerkschaft describes a labour union, whereas die Union, just some union, in a broader sense.

2) Those words mean more or less the same.

währen = to last, halten = to last (but it has many other meanings, like hold, keep, stop), dauern = to take time (Dauer = duration)

währen ends when it's over, halten ends when it breaks, and dauern ends when it's finished.