"Nobody knows what is going to happen."
Translation:Ingen vet vad som kommer att hända.
Why do you need "som" in this sentence? Doesn't "vad kommer att hända" suffice?
We use som as a pronoun to bind clauses, for instance:
- Jag har en syster. Hon är snäll. - I have a sister. She is kind.
- Jag har en syster som är snäll. - I have a sister who is kind.
Here, where English use "who", "which", "that", etc., vi use "som".
In the sentence "Ingen vet vad som kommer att hända", we need the relative pronoun "som" to bind the clauses together - but if we leave the "vad" out, we have nothing to bind it to. In English, the "what" takes responsibility for both of those things, but in Swedish, it results in the somewhat weird "vad som".
I'm not sure how clear that was, so if you have any follow-up questions please go ahead.
But in the section dedicated to those forms, we have for instance "Var nöjd med allt vad livet ger", and other sentences where only vad is used. What is different in them?
Oh yeah, I can see why that'd be confusing.
In "var nöjd med allt vad livet ger", the word "allt" takes the place of "syster" in my above example. Hence, the next word should be "som"... but we actually used to have "vad" as the reflective pronoun here for a very long time, just like English does. This lives on in selected fixed phrases, of which "allt vad" is one.
I would strongly advise you to always use "som" instead of "vad" in this scenario. And in fact, "var nöjd med allt som livet ger" is likely to be the vastly more common phrase, especially since that's the title of a song from Disney's The Jungle Book. :)
(Edit: For other pronouns, it's occasionally a bit more complicated. For instance, we can use "vilken"/"vilka" for "which" in certain cases, but it's a challenge to make that not sound very formal, and again, I would advise against it without a high level of proficiency.)