lens - What is the difference between the Canon 55-250 IS II and 55-250 IS STM lenses?

I am a beginner in DSLR, and would like to purchase another lens other than the kit lens (18-55mm STM) that came with my Rebel T5i/D700. After much googling, and reading of blogs, I have decided to purchase a 55-250mm lens.

I have found two options, either the Canon EF-S 55-250mm f/4-5.6 IS STM or the Canon EF-S 55-250mm f/4-5.6 IS II. The 55-250 IS STM is more expensive than the 55-250 IS II.

I did google for IS II vs IS STM. All of the blogs were technical ('cause I don't understand that "tech language") and I am looking for some "simple to understand" definitions, like does the image look sharp, will the background look blurrier, it's perfect for night photography etc.