The verb ser in Spanish is used when talking about something that doesn't change. For example, about who we are, where we come from, or something that always stays the same. If you want to say that you are from Spain or that your friend is tall, you need ser. This verb helps describe qualities that don't change over time, like age or nationality.
For example:
Yo soy estudiante - I am a student (and that's not going to change right now).
Ella es mi amiga - She is my friend (and that is something permanent).
Also ser is used to describe color, shape, time, and date:
La casa es roja - The house is red (and it always will be).
Hoy es lunes - Today is Monday (and it certainly won't change).
When you need to describe something permanent, ser is your best friend in Spanish!