What does this switch do?
That is NOT a &quot;circuit breaker&quot;, the Tele L unit is a SHUNT TRIP coil for a circuit breaker, in this case the breaker to the left of that unit, the DM100 C20, which is a 20A RCBO circuit breaker, meaning it is a Ground Fault (RCCB) and a circuit protective breaker combination.
What a Shunt Trip is for is so that you can remotely give a signal to it and it will purposely trip the breaker next to it, there is an internal connection. What you would do is apply power to C1 and C2, which would trip the breaker, then you can read whether it worked or not via 12 and 14. The handle is the Reset, so it should be left UP for this to function.
We cannot tell from here what you have wired to C1 and C2, that's specific to your site. If this is not a residence, it is sometimes tied to a fire alarm system, so that if something set of the fire alarm, it kills power immediately so that fire fighters do not get injured in fighting the fire. That's just a guess though.