‘-을/ㄹ 거예요’ is used to show that the speaker is guessing something. The subject is usually in the third person. When the verb ends with a consonant, use ‘-을 거예요’. When the verb ends with a vowel or a consonant ‘ㄹ’, use ‘-ㄹ 거예요’.
● 내일은 비가 올 거예요. (It will rains tomorrow.)
● 벌써 10시니까 아마 집에 있을 거예요. (She will be at home because it’s 10 o’clock.)