how do you know the difference between positional play and attacking play

When you are positionally superior you can easily start an attack... Although this was not the topic it is a very important thing especially for beginners like you and me

If they just develop their pieces and put them ready to go for some one target in your territory then you will know they are attacking but if they take time and take king to safety and tries to create targets and tries to accomplish the positional importance then you know that they are positional but there are some players who play both positional and attacking chess.. Like me probably.. 

Hope this helps you clear your confusion

Tactics is knowing what to do when there is something to do.
Strategy is knowing what to do when there is nothing to do.

Interesting

But I don't get that 'nothing to do moment.. What to do to have nothing to do

If you lose by dropping pieces, you are an attacking player.  If you lose but don't know why, you are a position player.

Just my two cents, but one difference might be that attackers fight for pieces. Positional players fight for squares / space. All good chess players switch back and forth between the two, depending on the structure of the game. 
I remember a game I played at our club many years ago. My opponent was an unknown, and after a dozen or so moves, I was totally boxed in with nowhere to go and nothing to do. He hadn't obviously attacked any of my pieces, made no mating threats, set up no combinations that I could see, but I was still ruined. I looked up and asked him his rating. "I'm a Master," he replied. Figured. Positional player.

No one understands this.. No one.. Not a single comment explains correctly.. But the best was from @Noone

you didn't explain it right either lol

Worst

50 percent correct 

One word: unratable(in a good way... Confusing me too

Read this

Chess that is "more attacking" versus "positional game" might not necessarily be opposites. There is a misconception that "attacks" are like Tal's famous Queen sacrifices, or Alekhine's tactics, or dangerous opposite-side castled pawn storms...

all of this is true sometimes, but not the only way to attack. Sometimes one can play in a very positional manner AND be attacking as well; they are not opposites! In chess, sometimes everything works together. 

As IM Jeremy Silman says, we need to "play the needs of the position." This might take years of chess experience to better grasp, but this means that the chess player should be looking for what the current chess position might harmoniously create instead of forcing your chess personality on it. Sometimes I'll play very positional games, other times I'll play highly tactical and sacrifice pieces left and right; and yes, sometimes I'll even play nice attacking chess that is also highly positional at the same time

+1 Also, this was one of the best responses that @tygxc gave, but I think it went over the head of most members in this thread. 

Let me rephrase this quotation in different words:

If you evaluate the chess position as one that requires a tactical attack, then you "know" you should be doing that. However, some chess positions, you can look forever and spot no tactics whatsoever...

that is the "nothing to do" and when you should probably be playing a more "positional move." This could be improving your worst piece; it could be getting your King slightly safer; it could even be something like centralizing one of your pieces. 

What is most certainly is, would be some "positional" concept and not trying to create a tactic out of a non-tactical position.

Good Positional Chess, Planning & Strategy Books for Beginners and Beyond...

https://www.chess.com/blog/RussBell/introduction-to-positional-chess-planning-strategy

I still don't get it.