This is a program for showing your text or other files, highlighting words of interest. You will see them in plain text format, with tag mark-up shown or hidden as in your tag settings. There are a number of settings and options you can change.
Its main use is to produce an aligned version of 2 or more texts, with alternate sentences or paragraphs from each of them.
See also: Viewer & Aligner settings, Viewer & Aligner options, an example of aligning