GIVE ANSWERS - Svenska

It's not that difficult.
First you have to know if the word is utrum or neutrum (en or ett). If it's neutrum (ett-ord) you have to look at the ending of the word. If it ends on a consonant, the plural is the same as singular: ett barn - flera barn.
If it ends on a vowel, you add -(e)n: ett äpple - flera äpplen.
If you have a en-word (utrum), the endings are -or, -ar or -er.
-or is easy, it's for all the words ending on -a, like en blomma - flera blommor.
-ar and -er is a bit more randomly, as a general rule "international" words have a plural on -er, while old swedish words (often with one syllable) go with -ar: en elefant - flera elefanter; en häst - flera hästar.

Hope it helps!
(As for the definite form of the nouns in plural it's another question...)

Its diffrent for every single word! for example: Ett val -> Två val = one choice -> two choices / En val -> Två valar = one whale -> two whales / Ett val -> Två val = one election -> two elections / Ett barn -> Flera barn = One child -> several children. However there are some rules that can be applied for some words. But it wont help much! Good luck!

Utrum & Neutrum are the two grammatical genders in Swedish. Nouns and pronouns are divided amongst them depending on whether you put "en" or "ett" in front of the word. "En bil" is Utrum, and "ett tåg" is Neutrum.

As for the plural form, it unfortunately not as simple as in English. There are several different plural endings and each noun uses a specific ending to make the plural form. Native speakers know them by heart and to learn which ending that goes with which word you are unfortunately going to have to learn the declension for each word.