What is my circuit breaker capacity load
This is a 63A, C-curve breaker
On IEC-style miniature circuit breakers (MCBs), the primary characteristic designation consists of a letter followed by one or two digits.  The letter indicates the trip curve of the breaker, or more precisely its magnetic trip setting. A B curve would be used for sensitive loads with little inrush, while a C curve breaker like yours provides a good general purpose compromise, and a D curve is used for very high inrush loads like some motors, transformers, or very large banks of lighting.
The numbers, then, give In, the nominal rated current of the breaker.  Pulling more than In for a significant period of time will eventually trip the breaker; loads less than In are permitted, although the wiring regulations in your country may require a derate (say, 80%) of the load if it's to be left on continuously (say, more than 3 hours at a time).  The wiring protected by the breaker, therefore, needs to be able to handle In without heating excessively as a result of that current, so that the breaker can act as a &quot;weak link&quot; and trip to protect the wiring from an overcurrent before the heat from that overcurrent event can start a fire somewhere in a wall.
In your case, your breaker is 63A; this is a common size for a distribution board main breaker/switch in a housing unit (house or flat) in European countries; if more power is required, the unit generally will be connected to two or three phases of electricity instead of a single phase.
As to those other markings...
The other markings on your breaker are meaningful, but not as relevant to most folks.  The 400V is the maximum nominal AC voltage the breaker can safely switch or interrupt; applying the breaker to a higher-voltage circuit will cause the breaker to get blown up by the higher-energy arcs produced by the higher voltages involved.  The &quot;6000A&quot; number you see on the breaker is a similar rating, only for the amount of current that could potentially flow in the event of a bolted short on the protected side of the breaker. If the wiring resistance of your house's and electric utility's wiring wasn't sufficient to limit the short circuit current to less than 6000A , then the breaker would be be considered underspecified as it'd be liable to blow up if a sufficiently large short was presented.  Again, this is due to arc energy issues; however, only your utility can tell you if that interrupting rating on your breaker (especially your main breaker) is sufficient for the service they are providing, as the maximum short circuit current the utility can provide depends on the size and length of their wires.