Cuando hay que usar 'ser' y cuando 'estar'? / When do I have to use 'ser' and 'estar'?

Ser and Estar are similar verbs but they each have specific situations where they are used. In general, we use Ser when we are identifying ourselves or others as well as our nationality e.g. Soy Cristina, soy españolaWe also use it for descriptions or characteristics inherent to someone or something (e.g. Soy fuerte; el mar es azul) and when we refer to a fraction or period of time (e.g. es jueves, es de día). Furthermore, ser is also used when we assess something or someone (e.g. el español es facil). On the other hand, we generally use Estar when we are placing or locating people, things or situations (e.g. la calle está a la derecha; Maria está en el médico) and we we talk about the physical characteristics or mood of someone or something (e.g. estoy cansada; Maria está triste; tú estás sucia) - these characteristics are not inherent but rather, temporary in most cases. Estar is also used before 'bien' and 'mal' (e.g. we don't say 'soy bien', instead we say 'estoy bien'). Moreover, Estar indicates the result of an action or the end of a process (e.g. está roto), as well as an action still happening when used with the 'gerundio' (e.g. esta caminando). There are more cases specific to each and other cases were both can be used, but this provides a useful guideline for the most common scenarios where these verbs are used.