Kitten sucking on clothes

I adopted a 2 month old kitten today. She's beautiful, naughty, and curious! And is also sweetly sucking on my clothes... Any tips on how to address it?

Also, I'm wondering about her litter box. I got a closed one with a door. The adopting instructions were to keep the box's door open at the first days, but it won't stay open. She sniffed the box and inspected it, but still hasn't used it. Will she know how to get in and use it?