Once you have completed telluric calibration (not before!), you are ready to combine the frames into a 1D spectrum. On the "Combine" tab, select the object(s) for which you intend to generate 1D spectra, and click "Combine to 1D." This procedure will average together the individual orders from all exposures on a given object, weighting optimally by signal to noise ratio. Then the orders of the combined spectrum are merged, again with inverse variance weighting, onto a single grid. The final output spectra are stored in the redux/FSpec subdirectory by object name. The files Objname_F.fits and Objname_E.fits are the flux and 1 sigma error spectra, respectively.
The FITS headers are modified to include the standard CRVAL1 and CDELT1/CD1_1 keywords for the wavelength solution at this stage, so any program can be used to inspect the output. Within IDL, you may wish to use x_specplot, which is a convenient spectral GUI distributed with xidl.