When do I use the verb 'ser' and when do I use the verb 'estar'?

Good question, they both mean to be. 'Ser' is for permanent states, for example, 'soy Ben', meaning 'I'm Ben'. That will always be my name, so we use 'ser'. 'Estar' is used for temporary states or to state where you are located, for example, 'estoy lleno de comida', meaning 'I'm full of food', or 'estoy en Andalucía', meaning 'I'm in Andalusia'.