Many people are often confused by the different software options that Tableau offers. Essentially there are three tiers in the software options. Each having an increasing layer of of features which are also related to price. Additionally, your intention will also govern what software version you should incorporate into your analysis stack.
Tableau desktop offers all the full features of software. Your workbooks can be share locally. This version allows you the connect to different file types, create extracts of the data sources and save your Tableau workbooks locally and publicly. The only thing that is missing here is the data connection types. You will not be able to have a direct connection to a database or web and software APIs.
Tableau Reader allows you to read the Tableau file types. If you want to share your workbook by sending a file, the receiver will need a Tableau reader to open the document. Without the reader, you may need share it publicly or convert the workbook into a PDF format.
Tableau Server allows users to save workbooks securely across the organization using a secure server. This eliminates the need for a user to have to share the workbook publicly. However, this comes at additional cost.