Question: how to use zdl with gzdoom?
Answer: Extract and open the ZDL folder.
Run ZDL.exe.
Click on the Settings tab.
Under the Source Ports/Engines section, click the Add button and then browse for the gzdoom.exe.
Under the IWADs section, click the Add button and then browse for your IWAD files (Doom. ... 
Click on the Main tab.