Ser vs. Estar
There is only one verb for existence in English: to be (I am, you are, he is...)
One of the perplexing features of Spanish is that there are two verbs that mean "to be", but they're not interchangeable. As a novice learner, this topic was very frustrating for me.
But these resources should help you to avoid the confusion and figure out how to use these two fundamental verbs correctly. It's really not as hard as it might seem. I hope that you master the difference between ser and estar faster than I did back before the Internet existed!
Online activities from the Realidades textbook
Book 1 Chapter 5B p. 258
Online activities from the Exprésate textbook
Book 2 Chapter 2B p. 62 (Summary of uses)
Practice with Ser and Estar - More practice with Ser and Estar
Detailed grammar explanations with self-correcting exercises
Online practice and games
Videos and interactive activities to learn Spanish online
Video interviews, podcasts, and grammar explanations
Ser vs. Estar Practice
Ser vs. Estar
Music videos to help you learn!