Do you have a simple explanation about ser and estar?

On of the worst things about learning Spanish is that there are two verbs for to be.  This is a big unesesary complication but you will never speak Spanish well unless you can use "ser" and "estar" correctly.

For example you use "ser" for professions.
Soy profesor - I am a teacher

Estar is often used for states:
Estoy cansada  - I am tired.


There is a good guide here

You can practise the present of SER here

You can practice the present of ESTAR here

They are very irregular verbs:
You can see the conjugations here.
Estar  Ser