I recommend only have one of them on to start (click B, C, and D so they're turned off) and just messing with the different options for envelops and filters. After that, start trying to combine them little by little to make more complex sounds...
The B, C & D operators actully have their volume down to zero by default, so turning them off doesn't actually do anything at this point
I think going straight to the filter/envelope section is kind of missing the point of Operator, because while the majority of synths use what's called
subtractive synthesis, the Operator uses a method called
frequency modulation synthesis (or "FM" for short). Learning to combine the A/B/C/D operators (they're technically oscillators, but thanks to Yamaha, they're called "operators" on FM synths...) is the whole point of this thing - if you just use the filters and envelopes, you're just using it as a regular subtractive synth - not that they're not there to be used, just that there are far more interesting options on that front.
Also: FM is fucking hard compared to regular subtractive stuff - it just isn't very intuitive in the same way, and changing the operator routing will produce often some unexpected results, for example. Just saying that this is definitely not the first time someone's been slightly intimidated by the mysteries of frequency modulation
Btw, there's loads of informatin in Live's own manual regarding Operator, even if it doesn't directly teach you how to use it. I'd still read it first.