Grammatically, this is a type 0 conditional, but semantically, the meaning is closer to a type 1 conditional which expresses a single condition and result. Examples: Type 0 - General truth or repeated condition and result. If (whenever, each time) that water is heated to 100C, it boils. Type 1 - Single condition and result. If you heat the tea kettle, the water will boil in a few minutes. The text in question: You need to study for your finals if you want to get good grades. Variations: Type 0 You need to study if you want to get good grades. Type 1 You will need to study for the finals if you want to get good grades. You will need to study if you want to get good grades next month. Type 0 with type 1 meaning. You need to study for the finals if you want to get good grades. Is this natural? Yes, people say this all the time.

You are right: it is a zero conditional, with a present simple on both sides. A first conditional would be "If you want..., you'll need to...". The difference is quite subtle, but a zero conditional would refer to a general truth whereas a first conditional would refer to a more specific future event.

It is a 1st Conditional because it refers to a possible (but not guaranteed) situation in the future. Just because you study hard, doesn't mean you will get good grades... Unfortunately haha. Zero Conditionals are only for facts, such as "If water gets cold enough, it freezes", because it is always the case.