The difference between ser and estar are: *Ser *is used to express what a person does or is in his/her life. For example: Él es mi hermano mayor. He is my oldest brother. Juan Carlos es mi novio. Juan Carlos is my boyfriend. Yo soy un estudiante. I am an student
However,
Estar is used to express that a person is doing something. Yo estoy escribiendo means I am writing. Ella esta enferma. She is sick.
If you need more examples: SER Yo soy la maestra de este salón. I am the teacher of this class. Tu eres una persona importante para mi. You are an important person to me.
ESTAR Ella esta comiendo saludable. She is eating healthy. Ellos estan cantando mi canción favorita. They are singing my favorite song.
I hope it clarify your doubt. 😀
Thank you very much Genesis, all clear now 😀