It depends what you have in mind for your bathroom and what price you want to pay.
Normal shower curtains are made from waterproof synthetic material like polyester and vinyl. They are generally cheap and cheerful and not such a big expense that you won’t be able to change them often if you get tired of the design. They tend to last a long time because the material holds up well to getting wet.
The swankiest luxury shower curtains are not made of water proof material but normal fabric - you keep them outside the bath and have a waterproof inner curtain which keeps the water in the bath as you shower.