This dialog allows you to save vector data in various formats using GDAL/OGR.

From the Format list you can select the destination format (as advertised by OGR).
At Save as you can enter a destination files name or select one using the Browse button.
In the Encoding list you can define in which encoding the data should be saved.
Using the CRS you can select a CRS into which the data about to be saved should be reprojected.
OGR also has various options for the different formats it supports. Use the datasource creation field to set the datasource options and the layer creation options. Enter one options per line (e.g. SPATIALITE=yes in the datasource to create a spatialite database using the SQLite driver).

See OGR Vector formats for a list of supported formats and the available options.