Question about reading hand ranges and equity
I am currently reading Professional Hold'em by Ed miller and in the equity part of it, he explains the math and then gives a short cut: "when considering your opponents range of hands, think about the hands you are a big favourite over to and think about the ones you are a big underdog to. If his range primarily contains hands you are a big favourite to, your equity is probably good."
So, for example lets say I have a middle set and I think villain has either straight draw, bottom set or bigger set than mine. So in this case I lose to two of his possible holdings, does that mean I should fold if he raises me? I apologize if this is a silly question, it looks really straightforward but I'm concerned with the math. Because him having a straight draw and having a set aren't the same possibilities right? so when we give them the same possibility, wouldn't we be wrong? I'm fairly new to poker so all of this is very new to me and the math of it looks scary. In the same book he briefly talks about finding his possible ranges and calculating my equity from then on based on his possible holdings in percentage. Can people actually do this? I can use hold em simulators in computer but I'm asking about the live games. Thanks for any input guys.
Also whats the best way to learn more about equity? Any book recommendations?