In Spanish there are two verbs for "to be": ser and estar.
Ser is used for more permanent/physical/personality actions,
estar is used for temporary actions. ?
How you feel and where you are, always use the verb ESTAR."
NOTE: General Estar Rule
Estar is used to indicate temporary states and locations. If the general rule doesn´t suffice, think of the acronym PLACE, which stands for Position, Location, Action, Condition, and Emotion.
Position: is the physical position or posture a person or thing is in.
Mi abuela está sentada.
(My grandmother is sitting down/seated.)
Yo estaba acostada cuando me llamaste.
(I was lying down when you called me.)
Location: of someone or something describes where it is permanently, temporarily, actually, or conceptually.
El baño está a la derecha de la sala.
(The bathroom is to the right of the living room.)
Estamos en el café ahora y estarémos en el cine en 20 minutos.
(We are at the café right now and we will be at the movie theatre in 20 minutes.)
Mi abuelo está en la luna.
(My grandfather is out of it/lost.)
NOTE: Exception for Parties
This is a big one: The location of an event or party is described using SER. Not ESTAR!
La fiesta es en mi casa. (The party is at my house.)
Action: used to describe an ongoing action using the present progressive tense.
Estoy lavando los platos sucios.
(I am washing the dirty dishes.)
Estamos leyendo los periódicos.
(We are reading the newspapers.)
Mi bisabuelo está muerto.
(My great-grandfather is dead.)
NOTE: Death is Ongoing Action
In Spanish, death is seen as an ongoing action, not a permanent state, thus you use the verb estar and not ser.
Condition: Physical and mental conditions are described using estar.
Estoy tan cansada esta mañana.
(I am so tired this morning.)
Mis niños están enfermos hoy.
(My children are sick today.)
Mi madre está un poca loca.
(My mother is (acting) a little crazy.)
Emotion: How a person is feeling at a certain moment is described using estar.
(I am sad.)
Ella está contenta porque recibió unas flores de su novio.
(She is happy because she received some flowers from her boyfriend.)