For the 330 ml size, the print-ready layout is 2591 × 1134 px at 300 dpi (219.4 × 96 mm with bleed). Upload one picture for the whole layout or one for each side; the editor shows each side's size.
Which materials can I preview the drink can in?
Glossy metal, Matte metal. Switch between them on this page and in the 3D editor; your artwork and the print PDF stay the same.