A look on the application can be taken here:

DC analysis (2:47min) guidance in performing the most simple simulation
Introduction 1 (4:29min) about the first steps with the application
Introduction 2 (3:38min) about working with the application
a little example (7:14min) by Elias Monteiro
Filter (5:32min) creating a 15th order Chebyshev lowpass filter
HB analysis (4:59min) demonstrate a Harmonic Balance simulation
Subcircuits (6:42min) embedding of circuits into a parent schematic
Tuning (5:31min) how to change component values with sliders
Optimizing (8:32min) automated optimizing of a stub filter
QucsTransline (4:26min) the transmission line calculator
Optimizer (10:36min) design of a diplexer using the circuit optimizer
EM simulation (15:54min) transfering a circuit automatically to a layout and performing an EM field simulation
EM simulation (12min) Create layouts for EM field simulation
Playlist many nice video tutorials in Japanese


schematic editor
DC bias shown within the schematic
optical telecommunication system
layout editor for electromagnetic field simulations
interactive formula sheet
running Octave scripts
transmission line calculator
component designer
filter designer
attenuator designer
PCB layout with KiCAD