Questions & Answers about Tôi sẽ gọi điện cho mẹ sau giờ làm.
Sẽ is a future marker. It shows that the action will happen later, similar to will in English.
- Tôi gọi điện cho mẹ = I call / I am calling my mother
- Tôi sẽ gọi điện cho mẹ = I will call my mother
Vietnamese does not always need a future marker if the time is already clear from context, but sẽ makes the future meaning explicit.
Gọi điện specifically means to phone / to make a phone call.
- gọi by itself can mean to call, but it can also mean to call out, to summon, or to name
- gọi điện makes it clear that this is a telephone call
So in this sentence, gọi điện is the natural way to say call someone on the phone.
In gọi điện cho mẹ, cho marks the person who receives the action, so it works a bit like to in English:
- gọi điện cho mẹ = call mother / call my mother
- more literally: make a phone call to mother
In many Vietnamese sentences, cho can also mean for or to give, but here it introduces the recipient of the phone call.