The Data View window shows the variable names and column header, and each individual row beneath represents an observation within the dataset.
This window behaves more or less like a typical spreadhseet table. You can edit values manually, or create new values with various analytical and processing functions.
The Variable View window is the other tab on the main window. This window allows you to add or edit details about the individual variables in your dataset. Variables are identified by type (string, numeric, etc.) and you are able to add labels and formatting options in this window.
The Syntax Window provides an optional way to run analytics and processes within SPSS and functions like a command-line interface.
This may be especially be useful for keeping track of multi-step processes when performing quantitative analysis. The syntax file can be saved as a text document and help you communicate workflows with collaborators and support research reproducability.