How does selling at a loss work?

Last year I made a good amount of money on GME, and at around the same time I bought ARKG. I still have the ARKG which just continues to plummet, and I'm looking to sell.

I'm reading that you can sell at losses to offset your gains for taxes. Would I be able to do this? Does it have to be during the same calendar year? I haven't filed my taxes yet.

Basically I am looking for the best way to get out of ARKG at a $6000 loss.

Thanks for the help, and let me know if I should post this somewhere else.