The form -(으)ㄹ게요 is a rather simple form to let others know your decision or intention. You can also use it to make a promise to someone to do something. Thus, it is quite similar to -겠다, but the form -(으)ㄹ게요 is generally used in spoken language among friends and family. Yet, it is a simple form to use that can really help you express yourself in Korean.
The form -(으)ㄹ게요 you use to tell another person what you decided to do or simply what you are going to do, somewhat like a promise. Although, you can also use it to make an actual promise to do something. So as you can imagine, this is a rather useful form to master. However, this form is mainly used in spoken language and you use it generally with your friends and family.
가: 일이 있어서 가야 해요.
나: 그럼, 저녁에 전화할게요.
A: I have work to do so I need to go.
B: Then I will call you in the evening.
How To Use
The form -(으)ㄹ게요 is not difficult to use, but there are a few things you have to keep in mind. Conjugating a verb with this form is not difficult at all. The form follows the ‘batchim/no batchim’ rule and you just need to keep in mind that a ㄹ batchim is treated as a ‘no batchim’. Of course, you also need to pay heed to the irregular verbs.
You can only use the form -(으)ㄹ게요 with verbs, you cannot use it with adjectives. For adjectives, though, you can use the form -겠다.
As you know you can only use the form with close friends and it is mainly used in conversations. Besides this, there are a few other restrictions to keep in mind. The form always refers to the intentions, will of the subject and that subject can only be the speaker (you). Furthermore, the form cannot be used in questions. It is a statement of your intent after all. The form is quite similar to -(으)ㄹ래요, but the latter cannot be used to make promises.