Positional players are players whose predominant style is to play solid, "quiet" chess. Capablanca was famous for his ability to convert the smallest of advantages into a win; and for being nearly unbeatable (during one 10 year period he never lost a single match or tournament game). He's probably one of the strongest endgame players to play the game, and he'd typically create that small advantage (a slightly better position, for instance), then exchange into an ending where he'd convert it into a win.
Tal was tactical chess personified: aggressive attacking chess, and lots of amazing sacrifices and combinations.
Top level players like these are masters of both positional play and tactical play - but what shows through more often in their games is their stylistic preference for either quieter positional play, or aggressive attacking play.
I think the difference is easier to see in the old GMs like Capablanca, Alekhine, Nimzowitsch, Marshall, Lasker, etc. Nimzo and Capablanca were positional, while Alekhine, Lasker, and Marshall were more tactical.
I don't quite understand the difference. I understand Carlsen and Capablanca are examples of positional player and Kasparov and Fischer are Tactical but when i watch them play, all i see are good moves involving good tactics and the position of the pieces.