To what I know, DC coupling can be used for both AC and DC.
AC coupling is used for AC only.
how is the circuit look like when DC or AC coupling was used?
As you said DC coupling allows both DC and AC signals through, while AC coupling accepts only AC signals.
Fig1a shows a waveform containing both AC and DC. If the oscilloscope is DC coupled, then the waveform is displayed as drawn in Fig1a. If the oscilloscope is AC coupled, then the DC portion of the waveform is blocked and only the AC portion is displayed as shown in Fig1b.