Mrs. Jennings' classes' webpage: Ser vs. estar
Simple tip:
When trying to decide whether to use ser or estar, ask:
Is is a place?
Is it a feeling or state of mind/health?
If it isn't, it should be ser. There are other rules, but if you ask those two questions you will get it right 90% of the time!!!!

Ser is used for characteristics (I am tall, I am nice), proffessions (I am a doctor), to say where you're from (I'm from Colombia).

Estar is used for places (I'm at school, or the party is at school), for mood or state of mind or health (I'm sick, I'm well, I'm sad), for the progressive (I am dancing, I am listening), for things that recently changed (the food is good today, or you are mean today)