This is a quotation from The Art of War 4.2.
Here's the original:
Here's my own translation that might help:
(1) Hence a good military man puts himself in a place where he cannot lose to the enemy, because the enemy has already lost. (2) The winning warrior has the win [and knows that] before he takes on the fight. (3) A losing warrior fights first and then seeks victory.
Reworded a little bit more:
(1) a good general only takes on battles he can win because he knows his enemy has already lost. (2) A good soldier only fights when he already knows he's going to win. (3) A bad soldier fights hoping he can win.
(We can't get anything nearly that pretty out of just the words that are written in the Chinese).
In response to your specific questions:
What is victory then ?
A victory in the above is a 勝 which basically means a "win". Here it would mean to win a battle or a match. The same characters are used for winning and losing in all sorts of games now.
Is Sun Tzu referring victory as the war with weapons only and battle after victory as something else?
I don't think the passage specifies whether you have weapons or not. Also, there's some question as to whether Sun Tzu is really about military tactics or also has a deeper meaning (this is debatable). But the basic idea is that idiots fight hoping to win but smart people fight when they know they're going to win. Worded negatively, don't take a fight you won't win. And attack your enemies when you know you will win.