Thanks for all the pointers.
I started by downloading the Eclipse CubeMX plugin and it works very nice on my MacOS system. Next step was to select the chip. For the STM32L053 nucleo board I guess it is: STM32L053R8Tx (not exactly sure as CubeMX lists so many parts).
Next step I was looking for the LED pin in CubeMX. I am trying first without going through the board schematics. So, the interesting list seems the pin PA5. What do you think? Maybe there is another trick to see the pin mapping for the Nucleo regarding blinky pins. So, my setup is as shown in the first screenshot.
Now, generating the code is a bit confusing for the first time. I will continue later there. Maybe you have some hints already where to look...
thanks in any case... the nucleo + openstm32 combination looks promising for scalable embedded development.