The two pieces of software we need are Icarus Verilog and GTKwave both of which are open source and publicly available.

sudo apt-get install iverilog
sudo apt-get install gtkwave

iverilog -o simple.vvp simple.v simple_tb.v

In this specific example, we are testing a Verilog module called simple.v. The test cases are contained in the file simple_tb.v, it can be named arbitrarily; although it is called modulename_tb.v by convention. We specify our output file to be simple.vvp

vvp simple.vvp

You should have something output in the form of

VCD info: dumpfile simple.vcd opened for output.
A is 1010, B is 0011.
A is 1100, B is 0101.

gtkwave simple.vcd

Once GTKWave has launched

1. locate the SST tab top-left of the screen and expand all
2. Locate the desired test case and click
3. Bottom-left of the screen should display a chart with Type and Signal. Drag whichever one you'd like to analyse over to the Signals tab