1) How do I tell if a package I have installed had been built locally or downloaded as a substitute?

2) There are a lot of packages with executable binaries in the bin/ subfolder in /gnu/store. However, if I didn't explicitly install the package, I don't have it in my profile and can't easily reach the binary without first looking it up in the store. Do I have to always "install" a package to be able to use run it easily?

Please, excuse my not-so-clear questions, I still don't fully understand how things really work in guix.