Yesterday         Today
I was sad.        I am happy. 
He was sad.       He is happy.  (HE/SHE/IT)
We were sad.      We are happy. (WE/YOU/THEY)

Simple Present - BE Verb - Lesson - Practice
Simple Past - BE Verb - Lesson

*Please note: these tenses are also called the present simple and past simple.

He was talking on the phone in 1998.