Swedish is a Germanic language, so unless you speak German (or Danish and Norwegian which are even closer related) it's no wonder you can't understand.

The difference between a / å / ä and o / ö is phonetic. Although they
look similar the letters are pronounced quite differently. The difference in pronounciation is greater than for example i / ï or u / ü. In short, we have a couple of more letters in our alphabet.
If you listen closely to a conversation in Swedish, and if you speak English, German, French or Italian - you will no doubt pick up on a word here and there that you recognize. Our language has been heavily influenced by several former super powers. The Germans during the Hansa trade days (14th-16th century, many nautical terms and things to do with trade), the French in the 18th century (words to do with culture, the arts and food), the Italians mainly through Latin and the church.
In English the influence goes both ways. The English language is littered by words which they inherited by the Vikings, and as the current super power in media and economics - American English is continuing to influence us and supply us with new words today.
Not a silly question at all.