It's just a table to help you determine your lead angle on the periscope when firing a shot using the sub itself perpendicular to the path of the ship.
If you want to hit a target right at 90* and it's traveling at 5kts, then you would turn the periscope towards the target and fix it at 6.5 degrees (353.5 degrees if it's coming from the left). When you see a part of the target you want to hit cross the centerline of the periscope, you fire your torpedo(s) and they'll hit.
What this chart in particular allows you to do is set it up so that you can hit the target at something other than 90* on.
For example, if you want to hit a target doing 9 kts at an angle of 80* (to reduce the chance of a dud, for example) then you would set the "lead" at 11 degrees towards the target.
Keep in mind you should still put your boat perpendicular to the track the target is traveling for this to work as it should.
Also keep in mind this particular chart is for the "fast" setting of the German torpedo. There are two other charts from what I'm seeing in this screenshot for the "medium" and "slow" settings (40 and 30 at the bottom).
This is similar to what has been dubbed the "Dick O'Kane Method" for US fleetboats. This chart is just a bit more "in-depth" than what we have on the US side.
I have a similar chart for 90* only in the gramaphone chart I made a while back using some formulae, etc. It's just not as advanced as this one.
Regards,
ElCid97