We can't use "will" for previous decision .Why do we use "will" in this sentence?

I will start my work tomorrow.

Question

We can't use "will" for previous decision .Why do we use "will" in this sentence?

I will start  my work tomorrow.

Answer

Hi, In English the verbs don’t change as they do in other languages such as Spanish or French.
To build a future sentence we use will + verb. For example:
Present: I speak English 
Past: I will speak English 
Present: He speaks English 
Past: He will speak English