An eyeshadow palette offers a spectrum of shades, usually within the same color group, or at least in complementary shades. At one end of the spectrum will be lighter shades (to highlight and brighten) then medium shades (for base shades on lids) then dark shades (for lining and defining). Sometimes they’ll have a mix of finishes, offering a blend of sheers and shimmers, sometimes an accent color for fun. Every palette is different and you should just go with your gut instinct in picking which one you think you’ll use most.
There are a few different types of palettes, but in general there are 3 main ones: 1) nudes/neutrals, which offer up flattering beige, brown and caramel shades 2) trend-driven ones that offer of-the-moment colors and 3) smoky palettes, designed to give you everything you need to create a smoky eye.