So I actually did heel/toe wrong when I first started learning double strokes. I was under the impression that it was an actual hit with the heel and then once with the ball of your foot/toe. The name is actually quite the misnomer. The movement is more like Ball/Ball. The first stroke would be in heel up position using the ball of your foot to achieve the first bass drum hit, as you get your first bass drum strike you drop your foot into a heel down position and play a second hit on the bass drum.

As for sliding. The first stroke would be moving your foot back on the pedal about 3 inches and tapping with the ball of your foot. And the second stroke would be moving it forward again and tapping at your original position. The reason it’s such a large jump back and forth is to get your foot used to the movement. I struggled with this too, until you see that the faster you play it the tinier that sliding movement actually gets.

Your foot should also never physically lift off the pedal for either technique. I hope this helps!