Cynthia,
It depends on your needs. At a minimum, you only need to download and install ArcGIS Desktop. Everything else is optional.
- If you are goning to be doing a lot of analysis or processing in a 64-bit environment, you may want to install the Background Geoprocessing module.
- If you will be working with significant transformations between coordinate systems, especially some of the newer, you would want to install the Coordinate Systems Data.
- If you will be working with enterprise databases you will need the Microsoft ODBC Driver 17, PostgreSQL 11.2 or appropriate version for your database and operating system.
- Likewise if you have a need and have appropriate licensing you can also install Interoperability, Data Reviewer and/or Workflow Manager.
- The Tutorials are helpful, if needed, but take a lot of storage space.
