Hi, I'm not a native speaker, but as far as I know, you would use être with verbs that indicate a change of state or movement. There is an acronym to help you remember them, "DR & MRS VAN DER TRAMP" (devenir, revenir, monter, rester, sortir, venir, aller, naître, descendre, entrer, retourner, tomber, rentrer, arriver, mourir, partir)