Learning English and vocabulary

Direct speech and indirect speech
Direct speech is the actually speech or word from the original speaker.e.g
1. The teacher said let us go home.
The first letter question must start with capital letter and it must alway be comma after said or equivalent.
Why indirect speech -: the verb to in the reported speech will determine the verb in the indirect speech e.g 1. The man declare mathematics is interesting (direct speech).
2. The man declare that mathematics is interesting.

Can will do with out English,is the end language in the world