We use indirech speech when we report what people said. in indirect speech, the tense usually goes "one step" back.
direct speech :
SIMPLE PRESENT TENSE
"I go to school every day"
PRESENT CONTINOUS
"I'm reading book"
SIMPLE PAST TENSE
"I went to school yesterday"
PRESENT PERFECT TENSE
"I have eaten fried rice"
MODALS
"I'll meet you tomorrow"
indirect speech :
SIMPLE PAST TENSE
"I said I went to school every day"
PAST CONTINOUS
"I said I was reading book"
PAST TENSE
I said I went to school yesterday
MODALS
"I said I would meet you yesterday "
