Knight's opening move I generally play 1.Nf3 as white . I actually wonder whether there would be any major difference if I play 1.Na3 instead of 1.Nf3 . I am a novice player . An illustration will definitely help me in understanding the reason behind this.
To answer your question:

Experience has shown that it is a good idea in the opening phase of the game to:


develop minor pieces (bishop/knight) quickly
and to occupy the centre (squares e4, d4, e5, d5 and thereabout) with pawns and/or to attack the centre with minor pieces


In this sense Nf3 is the better (and by far more popular) move. It attacks central squares (d4 and e5) and thereby prevents black from occupying the center with e5 immediately and potentially could also support a white pawn push to d4.

Na3 on the other hand does little to get hold of the center and in addition (as with any knight on the rim), it has fewer squares to go to: 4 instead of 8.



Occupying the center is important among others because it can:


limit the space of your opponent
allow pieces stationed around there to quickly reach other parts of the board as needed




For a novice player the first move(s) don't matter. It is highly unlikely that you win/lose a game because of the difference between 1. Nf3 and 1. Na3, rather because of some tactics later on. That's why it is recommend for beginners to focus on tactics first.