Congiuntivo is a very common verbe tense in Italian and its use can be difficult for non native speakers as it usually doesn't exist in other languages. It is usually used in dependent clauses and is usually introduced by the conjunction "che".
It is used in multiple situations, such as:
Expressing opinions: "I believe you are wrong" - "Credo che tu stia sbagliando"
Expressing a wish: "I wish you were taller" - "Desidere che tu sia più alto"
Expressing a hope: "I hope you feel better soon" - "Spero che tu stia meglio presto"
Expressing a doubt: "I doubt you'll be on time" - "Dubito che sarai in orario"
It is also used in impersonal expressions, for example:
"It is important that you study" - "E' importante che tu studi"