These three English words all mean "to make sure or certain" and are commonly confused, even by native speakers. This lesson will ensure that you understand the difference.
The phrase could have refers to something that was possible but did not occur in the past. In informal speech, it is contracted to could've, not could of.
English has two verbs, "to do" and "to make," that are both equivalent to a single verb in some languages, which makes it difficult for speakers of those languages to know which one to use in any given situation. Understanding the difference in meaning is key to knowing which verb you need.