Forming plural - So, if we have en klocka - klockor (def) - klockorna (indef) en pojke - pojkar (def) - pojkar
So, if we have
en klocka - klockor (def) - klockorna (indef)
en pojke - pojkar (def) - pojkarna (indef)
en kamrat - kamrater (def) - kamraterna (indef) - ?
ett ställe - ställen (def) - ställena (indef)

My question is - the vowels always change when forming plural (klocka, pojke)?

Question

Forming plural - So, if we have en klocka - klockor (def) - klockorna (indef) en pojke - pojkar (def) - pojkar
So, if we have
en klocka - klockor (def) - klockorna (indef)
en pojke - pojkar (def) - pojkarna (indef)
en kamrat - kamrater (def) - kamraterna (indef) - ?
ett ställe - ställen (def) - ställena (indef)

My question is - the vowels always change when forming plural (klocka, pojke)?

Answer

In short: Nouns are divided into 5 declensions (groups). Each noun group will have its own rule on how to bend the noun.

Here's some more info.
http://www.thelocal.se/blogs/theswedishteacher/2010/07/28/plural-endings/

Answer

There are certain rules to follow when forming plural. You can read about them here: http://en.wikipedia.org/wiki/Swedish_grammar

If you have any additional questions after reading that I'll try to answer them!