Howdy! Try to do the following:
1.) In your scene, go to the "Sources" window
2.) Then, right click inside the source window and select "Add"
3.) Select "Audio Input Capture"
4.) Rename it whatever you want, and click "OK"
5.) On the next window, click the drop down arrow and select your USB microphone.
6.) This microphone will now appear in the Audio Mixer Window and will be recorded by OBS. You can add filters to the Microphone within the Source Window, as well as delay and offset from the Audio Mixer. Make sure all the channels you plan on recording are not muted; and that the levels are set at the desired volume.
Hopefully this helps!
