I’m so embarrassed to ask this, and should kind of know due to my job (fairly senior corporate role) but I don’t... 
I’ve recently had a promotion and as part of my grade change I’m now eligible for the LTI scheme and have “PSUPs”.... Thing is, I don’t know what they are or how they work. Other than it’s a 3 year thing and that “it’s approx Xthousand” according to my boss.... Is it Xthousand per year but I can only access it after 3 years or Xthousand in 3 years? I assume the value might change though really I have zero idea at all... I’m totally clueless when it comes to shares and things!
I assume I’ll receive some literature at some point but can anyone tell me the basics please? I can’t ask at work - they would look at my like I had two heads if I did......