Cache clear for dummies: php opcache

I apparently need to make sure that my PHP has OPcode on in order to clear cache. I have looked everywhere and cannot understand the many different things I have found to fix this. I have NO idea what to do, am not thinking about compiling my PHP, which I don’t know how to do. In Drupal 7, this was so easy. Not at all sure why it became so hard in Drupal 8.

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