Which SNOMED CT files you use will depend on your use case. The SNOMED CT is more than just a flat list of codes and more like a database. The content includes concepts, descriptions, and relationships.
When you unzip the SNOMED CT US Edition release you will find the Full, Snapshot and Delta versions. The Full release contains all of the SNOMED CT data from the beginning of SNOMED CT. It will include the full history of every single concept (when it was first introduced, if it has been edited, retired, etc.). The Snapshot version is a “snapshot” of the current SNOMED CT data. This release will provide information if the content (concepts, descriptions, and relationships) is currently active or retired. The Delta release contains the new/changed content for the current release.
Which files you need will really depend on your use case. Are you using an electronic health record or system/application which was purchased from a vendor? If so, we suggest you contact your vendor so they can guide you as to which file(s) to use.
More information of the specific content of the different files can be found in the IHTSDO Technical Implementation Guide.