* "sten": This is a diphthong, meaning it has two vowel sounds blended together. It sounds like the "e" in "ten" or the "a" in "cat."
* "cil": The "i" in "cil" makes a short "i" sound, like the "i" in "bit."
So, the vowel sounds in "stencil" are two vowel sounds blended together ("sten") followed by a short "i" sound ("cil").