Use the definite article in French for expressions of liking, generalities, school subjects, languages, countries, body parts, time phrases and to turn an adjective into a noun. The indefinite article ...
Nous restons dans un camping. - We stay / we are staying on a campsite. On a reservé deux chambres dans un hôtel. - We reserved two rooms in a hotel. Je vais passer les vacances dans ma famille ou ...