Learn Russian: В будущем году мы поедем на море.

The word год has a special irregular form when used in the Prepositional case to talk about time. After the preposition в, it takes the ending -у. That is why we say в этом году (this year) and в будущем году (next year).

I usually learn that 'next' is следующий. Can I say в следующем году instead?

Yes, absolutely! В следующем году is actually the most common way to say 'next year'. В будущем году literally translates to 'in the future year' and is just another natural way to say the exact same thing.

Why do we use the prefix по- on the verb поедем?

Поедем is the future tense of the perfective verb поехать (to go by vehicle). With verbs of motion, adding по- to a one-way verb like ехать makes it perfective. It is the standard way to talk about a single, completed trip that will happen in the future.

Why do we say на море instead of в море?

In Russian, you use на with море when you mean going to the seaside or the coast for a trip. If you used в море, it would mean going literally into the water, like a submarine or a fish. Because it shows the destination of our trip, море is in the Accusative case (which looks identical to the Nominative case here).