Save 

Click on Save to save the current UV layout into a tiff file with the specified base name; the default is layout.tif.

Name field 

Change this if you want a different base name to the tiff file created.

Resolution field 

Set the pixel resolution for the tiff file here.

AA Lines 

Tick this to smooth out the jaggies in the saved image, though this slows down the creation of the file quite a bit.

Fill Polys 

Tick this to include the flattened color coding in the image.

Once created, the image is displayed; you can then use File|Save or Ctrl-S to save it to a different location if you wish, using a ".tif" or ".jpg" filename extension to select the format of the saved image.