the word shall and will be
Tommorrow, I shall buy some vegetable from the market. why cannot use Tommorrow, I will be buy some vegetable from the market.

Question

Answer

shall 是過時的英語。太文了。

你可以說
Tomorrow, I shall buy some vegetableS from the market.    
OR
 Tomorrow, I WILL BUY some vegetableS from the market.

口語從未說shall

Answer

You can say "I will", but it is a different expression.

You say "I will":
1. When you make up your mind on the spot. E.g. I'll get some vegetables then.
2. When you are waiting to make up you mind. E.g. If it rains tomorrow I won't go.

The example phrases you have given are kind of dead, as they don't really mean anything when not in context.

Answer

shall= you think it would be good to buy vegs tomorrow
will=you are going to buy them tomorow for sure

لا تفوّت فرصة تعلّم لغة جديدة وأنت مرتاح في منزلك. تصفّح مجموعتنا المختارة من مدرّسي اللغات ذوي الخبرة وسجّل في درسك الأول الآن!