What are the voltages noted next to the C-rates?
Battery capacity is commonly specified as a current times a time, often using units of Amp-hours.  For example, 10 Ah means that in theory the battery can deliver 1 A for 10 h.

There will be some current range where you can trade off time and current linearly, but that relationship will fall apart at both low and high currents.  Using the above example, you could calculate that the battery should be able to deliver 10 A for 1 h.  The math is correct, but you have to look at the battery datasheet carefully to see whether 10 A is a valid discharge current, and if so, whether that is high enough to degrade capacity significantly.

In battery specs, "C" is understood to be the theoretical one hour discharge current, whether the battery is actually capable of that current or not.  When the capacity is specified in Ah, then C is the same number although it has units of amps instead of amp-hours.

Now look at your chart and take the top line, representing a single battery, as example.  Cnom is the nominal single-spec capacity, which is 200 Ah.  This is further defined to be the 10 hour discharge rate, and measured according to a particular DIN standard.  The other Chours values are specified over different discharge times.

Although the snippet of the datasheet you show doesn't explicitly say so, the voltages in the column headings are almost certainly the terminating voltages for the discharge test.  Note that for higher discharge rates, like C1 (200 A), the ending voltage is lower.  This is because at this higher current, there is some drop due to internal resistance, and there is still meaningful charge left in the battery until its external voltage goes down to that level.  Basically, these are the voltages at which you should consider the battery discharged for the indicated current.