CSV Import/Export plugin allows you import CSV file with data to supported directory type theme and export data into CSV file from supported directory type theme.
After plugin purchase you can install plugin in a standard WordPress way.
In Plugins options screen click on Add New and Upload Plugin button. Next screen will ask you upload zip file with plugin. Select zip file with plugin downloaded from your profile dashboard.
CSV Import/Export plugin is intended to export and import data in one theme, do not use it for migration of data between themes because structure of each theme may be different