Ser is used when something is forever (never change). For example: "Yo soy humano" "Yo soy americano" "Yo soy sydney" Estar is used when something can change. For example: "Yo estoy bien" "yo estoy cansado" "yo estoy estudiando"

There are lots of resources online to explain this but briefly 'estar' is for temporarily states and positions of things. Ser can be used for essential characteristics of things. Like for emotions use 'estar' but for characteristics of a person use 'ser' E.g. Ella está tímida - this means at this moment she feels shy Ella es tímida - this means this is part of her character. She's a shy person normally.

Ser is use to define personality issues Estar is use to define places and moods

El verbo "ser" define, indentifica lugares, describe seres y objetos, valora, indica la materia de qué está hecho, indica el origen. El verbo "estar" sitúa en el espacio, indica el estado civil, habla de una acción en desarrollo, se refiere a estados físicos o anímicos, describe características de objetos y lugares.

It´s quite difficult to find a rule here but I´ll try to explain it. When you are describing how you are physically or in a behaviour aspect you will use SER. In the other hand if you are saying how you are currently you will use ESTAR. I´m going to show you with examples: I´m handsome = Soy guapo I´m older than you = Soy más mayor que tú I´m smart = Soy inteligente I´m ok = Estoy bien I´m tired = Estoy cansado I´m dating her = Estoy quedando con ella I´m running = Estoy corriendo Am I wrong? = Estoy equivocado? When you say "I´m 22 years old" you must say in spanish: Tengo 22 años. Is like I have got 22 years old, but we don´t have a SER o ESTAR form when we are talking about how old are we. I hope it has been helpful