Sé and Se may look similar but they have completely different meanings.
Not only one of them has the accent on the vowel “e”, but also the pronunciation is slightly different.
Sé is a reflexive pronoun for the 3rd singular person.
Use Sé when referring back to the subject of the sentence:
“Sara non fa che parlare di sè.”
“She keeps talking about herself.”
Se, on the other hand, simply translates to “if”, and it introduces the protase, that is the dependent proposition, in the hypothetical period.
Use Se when forming a hypothetical period:
“Se hai bisogno, sai dove trovarmi.”
“If you need me, you know where to find me.”