The validate command validates the resource on the top of the stack, using the current Scope.
Validation needs a lot of data: from StructureDefinitions on the resource itself, to data types, Extensions and ValueSets. It will look into your project (current folder) and any packages, wether dependencies or depenencies of dependencies (etc.) to find all these assets.
Validation will report any errors and warnings and information messages to the command line output.
> fhir validate
You can use your own terminology server or specifiy an additional profile to validate against. For more details on these paremters, see:
> fhir ? validate