i need to be a little more precise and less confusing. Like @ fungal_net said,every name of service ending with @ require a word after it. A service name ending with @ means instantiated service.
But the dance 66-enable, 66-env, 66-enable -F to apply the change is not mandatory for all instantiated service. A instantiated service as type Module need this dance but an instantiated service as type bundle,longrun,oneshot,classic do not need it.
Let me explain again by an example:
for the boot-user@ which is an instantiated service as type module:
% sudo 66-enable boot-user@ example # enable the service
% sudo 66-env boot-user@ example # configure the module part to suit your needs
% sudo 66-enable -F boot-user@ example # apply the configuration of the module
% sudo 66-start boot-user@ example # start the service
for the jackd@ which is an instantiated service as type longrun
% sudo 66-enable jackd@ example # enable the service
% sudo 66-env jackd@ example # In the majority of the case, we don't need to change anything from the service environment. This operation can be skipped.
% sudo 66-start jackd@ example # start the service
Hope it's clearer