The question refers to classical music and I think, for a newbie it´s a funny thing indeed: One and the same score, when played by different performers on the same instrument and in the same setting (e.g. classical concert) yields a different performance.
Obviously, when a Beatles song is covered by a metal band it will be a different performance, but I guess this is not what you refer to.
E.g. tempo. Often no tempo is indicated, the performer will have to choose a tempo taking into account what he knows about the piece. But even if a tempo is indicated e.g. allegro or tempo di tango that does not transform into an exact bpm number, one performer might like to play a little faster and another may choose to play the piece a little bit slower. And even when there is a bpm number, performers will not play the piece in that tempo. And even if they do, they will not: There might be instructions like e.g. Ritardando, Ritenuto, Rallentando, Deccelerando, Allargando all meaning something along the lines of getting slower. But how much slower? And how? Continuously, in steps? Linearly? Exponentially? The performer (or conductor of course :-)) will decide that on his own. And even when there is no tempo change indicated, the performer will often change tempo nonetheless. Here a little bit faster, there a little bit slower.
Wether you like the performers decision is subjective of course.
There are endless numbers of other parameters a performer has to choose, for e.g. a violinist might choose to play a chord just or equal or change the pitch of some notes so that the sound of intervals changes to be more consonant or dissonant, or a performer might add or remove slurs. On some instruments there a several possibilities to play one and the some note, the choice will change the timbre. Using an open string e.g. or not doing so. Or take volume for example. f means loud and mf means not so loud. But how much not so loud? Diminuendo: Getting less loud. But how much? How fast? And so on ...
So when you look closely it becomes extremely unprobable to hear the same piece twice by different performers. It's also probable that the same piece played by the same player won't sound the same, even the next week, and certainly after several years
Here are two extremely different versions of Bach Cello Suite No.1:
Look out for the differences.
Of course you need some kind of a trained ear (or eye) to recognize the differences, either by listening experience or performing experience or formal education. The more trained you are the more differences you will recognize, which might be a blessing or a curse :-)