There is a big rotating button on he top left where you choose how many and which tubes are concerned by the salvo shot. Besides that you have on the right a needle to decide for the spread angle.
If you fire a 2 torp salvo with a 2 degree angle, each will hit 2 degrees left or right of your aiming point. If 3 torps are fired, one will be on the spot and the two other 2 degrees left and right.
Edit : after re-read this is the layout of the slideout I have at periscope and UZO. In TDC viex it is down and not top. Couldn't remember as I don't use the TDC view since I have all controls as slideouts.