The verb strunta is usually combined with the preposition i to mean 'to not care about', 'to give up on' or 'to ignore'. For example: Jag struntar i det or det struntar jag i both mean 'I don't care about that'.
It's a phrase to tread carefully with, as it can come across as quite a strong and emotional phrase, but that depends a lot on context.
And there are some more vulgar alternatives, which you should avoid using around Swedish friends or colleagues unless you're very confident the context is appropriate: skita i is a variant of strunta i, but it literally means 'to shit in'.
Strunta i (and skita i) can be followed by many types of word. You can follow it with a noun or pronoun, for example: jag struntar i dem (I don't care about them), or han struntade i filmen (he didn't care about the film), or with an entire clause, which might start with att or with a question word such as hur, vem, or vad.
For example: de struntade i att han var berömd (they didn't care that he was famous) or jag struntar i vem hans föräldrar är (I don't care who his parents are).
But it can't always be directly translated as 'not care about'.
Strunta i can also mean 'to ignore' or 'to omit' in a more neutral sense, for example många struntar i att rösta (many people don't vote) or han struntar i att betala räkningarna (he doesn't pay the bills). However, in this kind of phrase there's usually a sense of judgment, implying that the subject of the sentence is ignoring something they shouldn't, being reckless or disobedient.
You will also hear strunta i used as an imperative or command, for example strunta i det meaning 'forget it' or 'never mind about that', or strunta i henne, which means 'ignore her' or 'forget about her'.
And a related word that's handy to know and fun to say is struntprat, which literally means something like 'something someone says that should be ignored', but can be translated as 'rubbish' or 'nonsense', for example Det är bara struntprat (that's just a load of nonsense).
Man kan inte strunta i att tänka om klimatet
You can't just not think about the climate
Jag struntar fullkomligt i dig
I really don't care about you