Questions & Answers about Tôi sẽ gọi điện cho bạn sau.
Sẽ is a future marker. It tells you that the action will happen later, not now.
So in Tôi sẽ gọi điện cho bạn sau, sẽ means something like will in English:
- Tôi gọi điện cho bạn = I call / I am calling you
- Tôi sẽ gọi điện cho bạn = I will call you
In everyday Vietnamese, sẽ is sometimes omitted if the future meaning is already clear from context, but including it makes the future meaning explicit.
Gọi điện means to call, especially to make a phone call.
Literally:
- gọi = call
- điện = electricity / electrical, but in this expression it relates to the phone
As a set phrase, gọi điện means phone someone.
A very common alternative is gọi điện thoại, which also means to call by phone. In casual speech, people may simply say gọi if it is already obvious they mean a phone call.