Learn Italian: Se il prezzo è troppo alto, non compreremo niente. - If the price is too high, we will not buy anything.

This is a classic First Conditional sentence, which talks about a real possibility. In Italian, just like in English, we often use se (if) with the present tense for the condition (Se il prezzo è), and the future tense for the result (non compreremo niente). You can also use the future tense for both parts in Italian, but present plus future is very common and sounds very natural.

Why do we need non before the verb if we already have niente (anything)?

Italian uses double negatives! When a negative word like niente (nothing/anything) comes after the verb, you must put non before the verb. So, non compreremo niente literally translates to 'we will not buy nothing,' which is the perfectly correct way to say 'we won't buy anything' in Italian.

Does troppo change its ending here to match alto?

No, in this sentence troppo is an adverb meaning 'too' (as in 'too high'), so it is invariable and never changes its ending. It always stays troppo. It only changes endings when it acts as an adjective describing a noun, like in troppe macchine (too many cars).

How do we get compreremo from the verb comprare (to buy)?