How do i switch tenses?for example present tense to past tense?

So I'm going to write a crt or most usually in essay format. My teacher said that we could switch tenses, but how? Can u give me an example? and can u explain it how to do it? I'm kinda of confused about this switching tenses. Cuz whenever i write an essay I usually use present tense for the whole essay and sometimes it kinda hard to do it. We;re gonna do macbeth essential questions later Thanks in advance
r u kidding me? i know that i mean a paragraph example of switching tenses