Questions & Answers about Гулять в парке полезнее, чем сидеть дома.
Russian often uses the infinitive to talk about actions in a general way, similar to English gerunds (walking, sitting).
- Гулять в парке = “(To) walk in the park / Walking in the park”
- сидеть дома = “(To) sit at home / Sitting at home”
In this sentence, each infinitive phrase functions like a noun phrase, describing an activity. You’re comparing the two activities:
- Гулять в парке – subject/thing 1
- сидеть дома – subject/thing 2
- полезнее – tells which one is “more useful/healthier”
Using nouns like гуляние or сидение would sound very bookish or unnatural here. Native speakers strongly prefer the infinitive constructions.