Snapshot replication consists of taking a copy of an object on the publisher and transferring it to a subscriber. The transmittal of the replicated data is an all-or-nothing proposition: Although you can filter a snapshot horizontally as well as vertically to limit the data it captures, there's no support in snapshot replication for propagating incremental changes. You use transactional or merge replication for that.
SQL Server implements snapshot replication via the Snapshot Agent and the Distribution Agent. The Snapshot Agent takes care of creating the data and schema snapshot that will be propagated to subscribers. The Distribution Agent handles taking the snapshot and applying it to subscribers.