My video screen is black; originally my zoom app was set-up for phone conversations without video

My video screen is black on my laptop's ZOOM app, showing only my name at the bottom left hand corner.  When using my latop as a telephone at my former work location, the ZOOM app was originally set-up for phone conversation only, via a static phone number, without video capability.  I think or I hope there's a 'preference default setting' in the ZOOM app that needs to be changed in order to switch-on (or, engage) my laptop's video cam ....  Can anyone help me with this in order to engage my cam?