Let's take the common watch circuit. Conceptually it's just like 5 components: crystal, a few capacitors, a NOT gate/transistor/amplifier. Introduce 180-degree phase shift at the 32.768k target frequency and bam, oscillator.
Except not really. A clock is expected to have a drift in the region of 100 ppm (or 0.001% error), or lose a second per day or so. That's the hard part, building something that accurate and consistent.
There are also startup specs, power specs (less power is harder. More power helps startup....) etc. etc.
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If you just need something to oscillate back and forth randomly, try making a noise generator lol, it will oscillate wildly at many frequencies, one of which might have been the frequency you wanted.
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The 555 timer is perhaps the easiest oscillator for a beginner if you are willing to put up with +/-10% drift. It's honestly good enough for far more applications than you might expect.
Even without the premade chip, a 555 timer is just 2x comparators (analog version of an If statement), a 33%/33%/33% voltage divider, and a capacitor. If Voltage > 66% input voltage, remove power from capacitor. If Voltage < 33% input voltage, add power to capacitor. Bam, you now have an oscillator that is accurate to the +/-10% capacitance values of your electronics kit.
Alas, modern circuits need to be faster and more accurate than the humble 555. But a beginner article about oscillators should be about the 555, rather than about opamp or transistor based oscillators.