Is the VCR/DVD one machine or two? If it is one combo machine, do the following:
Connect the converter box to the VCR/DVD and then run a cable from the VCR/DVD to the TV. So the order is: In from the wall to the converter, OUT from the converter and IN to the VCR/DVD, OUT from the VCR/DVD and IN to the TV.
If you have a VCR and a separate DVD player, you want to follow the instructions above using the VCR. Then you connect the DVD player directly to another input on the TV (if there is one). A DVD player doesn't need to be connected to the converter because a DVD player just needs to show its content on the TV (which doesn't require a TV signal).
Hope that was clear. If not, you can Google "Connect digital converter" to find diagrams and additional help. Good luck.