Ser or estar?

In Spanish there are two ways of saying to be.
Ser is generally used for things that don’t change too much – inherent characteristics of people or things. Some examples are marital status, height, occupation, size, race, nationality, sexual orientation, religion, and possession (es mío, es tuyo). We also use ser to tell the time (son las ocho), to give a value judgement “es obvio que, es evidente que” and (rarely) for the passive voice.
Estar is for things that change more often, like feelings, present circumstances, and locations. You can also use estar to highlight that a characteristic that would normally use ser is especially prominent at that specific time, you look very pretty today, “estás muy guapa hoy.” All locations use estar, even for things that don’t move, Madrid is in Spain, “Madrid está en España.” Estar is also used in continuous verb tenses. This means times when the action is still going on, so we’d use an -ing word in English. I am eating, “estoy comiendo.”
Unfortunately, there is an element of subjectivity with the rules and at times you will need to learn which verb to use as an exception. An example of this is that “es obvio que” (it is obvious that) takes ser where “está claro que” (it is clear that) takes estar.
Some words change their meaning based on whether you use ser or estar. One example of this is the adjective bueno. If you use ser with bueno, it means good as in a good person. If you use estar, it means the person is physically attractive.