Hello,
Thanks for your response.
Is the PGP key mandatory like to be completed before the conference ?
Or it is also possible to do it while I am at the activity?
It is completely optional.
You don't have to bother with it, unless you want to start contributing to Debian by maintaining one or more packages. In this case you need to sign your packages with your PGP key, for security reasons, and your key needs to be recognized by the other Debian developers, in order to make sure that it is you who built the package and not someone else.
For participating in the conference you don't need a PGP key.