Putting someone on a range is easily explained, but requires lots of practice.
Basically, when you start out a hand you put everyone at the table at any hand, then remove the hands that don't make sense with the actions they make. Let's say you're playing someone who has always been very tight and they open raise in a middle position. You can put them on AA, KK, JJ, TT, 99, AK, AQ, AJ, ATs. Maybe some other hands too, but lets stick with these for now. Everyone folds up to you in the big blind and you decide to call with your
So you see a flop and it's
Now your opponent bets half pot. What does this tell you? Assuming he isn't bluffing
you can draw some conclusions from this bet. You can remove AK, AQ, ATs from his possible hands leaving him in the range AA, KK, JJ, TT, 99, AJ. Then you compare your hand to his range and see if it's worth it to continue. You have the top pair, but all the hands he can have in this position except TT beats you, so you fold.
Of course in this scenario it's most likely a continuation bet and doesn't tell you much at all about his hand, but it's just to explain the concept of ranges. And also you need to consider pot odds
and all that stuff, but again, it's just for explaining ranges.