This is a very simple example which samples ADC channel 0 at 1Hz. This ADC channel is mapped to the module's pin PD0 (Pad #2) which is available in the WSTK expansion header on pin 4, right next to the VMCU pin.
The ADC reference is configured as Buffered VDD with the following line in the hardware configuration:
<adc reference="2" />
Any analog signal referenced to the same ground as the module and with a dynamic range of 0V to VDD (which is 3.3V if the kit is powered from USB) can be measured.
The ADC has 12 bits resolution and this example prints out via UART0 the raw ADC result value without any mathematical conversion so you will see values between 0 and 2^12-1 = 4095.
To test this example you can simply put a wire from PD0 to GND and see the result go to 0...
... or wire PD0 to VMCU and see the result go to 4095.
If you don't have a jump wire then it's easier to use the expansion board with the analog joystick. The project 'adc_example_joystick' samples PD4 instead of PD0 at a higher rate of 10Hz and prints out the raw value. You will see it changing when moving the joystick as well as an 'X' when you move the joystick left or right as shown in the screenshot below. The joystick in the expansion board has 9 measurable positions and uses different resistor values to create measurable voltages in each of the 9 positions. A block diagram is available in UG172 - WSTK User Guide.