Questions & Answers about Hvis jeg nyser meget, bliver min næse helt rød.
Because Danish main clauses follow the verb-second rule.
Here, the sentence starts with the subordinate clause Hvis jeg nyser meget. That whole clause takes the first position in the sentence. In the main clause, the finite verb must then come next, so you get:
Hvis jeg nyser meget, bliver min næse helt rød.
Not:
Hvis jeg nyser meget, min næse bliver helt rød.
This kind of inversion is very common in Danish after anything placed first, not just after hvis-clauses.
Hvis usually means if.
In this sentence, it introduces a condition:
Hvis jeg nyser meget = If I sneeze a lot
Depending on context, English might sometimes translate it more naturally as when or whenever, but the basic Danish word here is still hvis.