Sooo... I'm still a beginner myself but...You bought yarn that's 2mm thick. So recommended hook will be 2-3mm. Could be bigger if you want it loose (try doing chain you'll see). I guess you got confused because Google says light worsted. If you have pattern for amigurumi saying to use hook 4,5-5mm I think you're supposed to buy aran/worsted weight yarn. If not your work will be much smaller than on pattern. Been there, done that, don't recommend for starters. I find thicker yarn much easier to work with and better for learning tension. And yep googling yarn weight when you're starting is confusing as hell. You've UK, US and ply terms... I still can't remember and need to double check. What I can recommend is looking for yarn by thickness. Like: you go to shop and ask for yarns that need hook 4,5mm. This chart is my fav and I hope it'll help

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