As you know, both of the verbs mean 'to be', which is quite confusing! However, in Spanish unlike English, for different contexts and meanings, we use a different version of 'to be.' Ser is a verb which implies permance, or something very long term. We use or interpret it in this way. For example:Soy inteligente- I am intelligent.We use 'ser' as it is describing a characteristic of a person. This implies something more long term and more permament, than for example:Estoy harto - I am fed-upThis is a temporary state of feeling and being, unlike a characteristic.Another key difference is we use estar for place:Eg: Estoy en el estadio- I am in the stadium.