In simple terms, Pimples, also known as Zits are just one infection of a single pore. Acne is several infections in various pores.
As you can see, Acne is a common term; it can combine whiteheads, blackheads, pimples and so on. There is no big difference between acne, pimples, zits, etc. They are different words but they are almost the same thing.
In other words, Acne is just a lot of pimples together. Pimples are individual breakouts where as if you get a lot of them and they keep coming back, that is acne. So, Pimples are periodic, and acne is a chronic condition. If a person, break out every so often, then it is pimples, but if that person stay broke out it is considered acne.
For more severe acne, which is nodular or cystic acne, you should seek advice from a dermatologist. But, please keep in mind, whatever you do, DON’T pick your pimples, because it will leave scars.