You know you're a geezer if.....you know how to operate a turntable.
Boy, do I feel old!
What you see in your Zenith is a record changer or automatic turntable. You would put a record, (or a stack of records) on the spindle. The L shaped arm you see is a sensor that would determine if there were records waiting to be played and it was lifted and swung out of the way to load records, then swung back over the records, dropped onto the stack and would drop lower with each record played. The spindle has a lever which holds the records up off the platter until called for. There is a mechanism within the turntable that determines the position of the tonearm and the sensor arm and either drops the next record onto the platter, moves the tonearm off the rest, positions it over the start grooves of the record and slowly drops the needle onto the record surface, or it will sense that there are no more records to be played and will lift the tonearm, return it to the rest and shut off the platter. Usually, there was an alternate spindle provided with no lever. You could remove the automatic spindle by pulling it up and out and replace it with the shorter manual spindle which did not have the record hold/drop mechanism. This was preferable for the serious audiophile in that automatic record handling was extremely damaging to the records themselves. All the high end turntables were manual only. Automatic turntables like yours were a consumer device and were considered low end. Most were manufacturered by BSR or Garrard and fitted by the electronics manufacturer, (like Zenith), to their consoles.
There will be two levers on your turntable. One will select the platter speed, typically 33 1/3, 45, or 78 rpm. LP's such as in your picture were 33 1/3. Selecting different speeds would produce interesting variations of the music and was generally considered to be amusing. The second lever is used to start the platter and initiate the automatic action. With the stereo turned on and phono selected, moving the 3 position lever to the on position would start the platter turning. This position has a detent that keeps the platter turning till the lever is moved back to the off position, (either manually, or by the automatic mechanism sensing the end of the record). The same lever has a spring loaded start, or auto position which initiates the automatic action as described above. If you start the turntable without a record on the automatic spindle and engage the auto mechanism, the tonearm will lift off the rest and cycle back to the resting position, after which the turntable will shut off. If the record detector lever is held lifted, the turntable will think there is a record to be played and will drop the tonearm where the start grooves should be. Moving the tonearm to the center of the platter with the platter turning will engage the auto cycle mechanism with results depending on the position of the record sensor lever. No more records will return the tonearm to the rest and shut off the turntable. Keep in mind this process is entirely mechanical. The only electric circuits are the motor and the phono cartridge.
I would recommend you avoid stacking your records on the spindle, but if you choose to do so, it won't be fatal, especially for well used records. Place a record on the turntable, start the platter and move the tonearm over the start grooves, dropping it gently to the record surface. If all is well, you should hear real analog audio coming out the speakers. Enjoy!