Any pictures or advice. I guess I'm not understanding how or the concept.

Do you mean like this?

https://www.youtube.com/watch?v=V6Am7...layer_embedded

Or this?

https://www.youtube.com/watch?v=c9aJtO0VCqw

Or this....

https://www.youtube.com/watch?v=5IOgYuKUFao

Like tucking your pelvis under when you sit on the saddle?

If this is a problem while riding, then your saddle is set too high.

On the other hand if it concerns Belly-dancing then you're on your own.

This, I think, though your post isn't exactly self-explanatory. An old method for determining saddle height was to have someone hold the bike up while you sat on it with your heels on the pedals and pedaled backward. You raised the saddle a fraction at a time until your hips rocked, then lowered it until they stopped.

Or did you mean rocking your hips?

https://www.youtube.com/watch?v=tHWvZtvC0jY

https://www.youtube.com/watch?v=mLwvr9LzVw0

By the way- if you mean, side to side- that means your saddle is too high- but, I've seen people that rode like that, and rode very well, and rode long distances, and were completely comfortable doing it- so hey, whatever works.

Sorry I wasn't specific, I mean when peddling/riding in general I read that it's best to be in position such that you roll your hips forward (slight anterior tilt?).

As such, how is this supposed to look/done?

Try this ... sit upright on a hard chair with good posture, now suck your abs in. Now lean forward. Is that what you mean? That's more or less the correct way to sit on a saddle.

Focus on bending forward from the hips and trying to keep your lower back straighter.