qxaxis(y0, [x0 x1], xx) plots an x-axis with ticks at xx. (xx may be empty.)
qxaxis(y0, xx) calculates x0 and x1 from xx.
qxaxis(y0, [], xx) only draws ticks, not an axis line.
qxaxis(..., lbls) where lbls is either a cell array or numeric vector the same size as xx overrides the default tick labels. Labels are suppressed if lbls is empty.
qxaxis(..., ttl) adds a title to the axis.

qxaxis obeys settings from qticklen, qtextdist, and qaxshift.
qxaxis('t', ...) inverts the sign of these settings.

Either lbls or xx (but not both) may be a function handle in which case the labels are calculated from the tick positions (or vice versa). For example:
     qxaxis(0, @(x) (x/100), [0:25:100], 'Value (%)')

Without any arguments or with just a title as an argument, qxaxis tries to determine sensible defaults based on previous calls to qplot. Your mileage may vary.