Questions & Answers about Í júní eru kvöldin bjartari en í september.
This is because Icelandic is a verb-second language.
When a time phrase like Í júní (in June) is placed first, the finite verb usually comes next. So the order becomes:
Í júní + eru + kvöldin + bjartari ...
A more neutral order is also possible:
Kvöldin eru bjartari í júní en í september.
Both are correct, but the original sentence puts a little more focus on Í júní.
Kvöldin means the evenings.
The basic noun is kvöld, which means evening. In this sentence it refers to evenings in general during June and September.