i think what you arent aware of yet is that a certain type of hand plays exactly the same way most of the time, and that understanding these 'lines' is what putting your opponent on a range of hands is all about.

If someone check/calls all the way to the river and then open shoves when the draw hits, then you know he probably has it. Why do you know this, because thats how microstakes players can play their flushes.
In essence you know the range of cards your opponent has. In a lot of examples the information you have isnt as clear or your hand is much mor marginally strong, 2nd pair for example.

What you dont know yet is how lots of these other hands play after the flop, and that will come the more hands you play.