heel and toe is a method to rev match whilst maintaining pressure on the brakes - ie, approach corner start braking with ball/left side of right foot, clutch in, downshift, blip throttle with heel/right side of right foot whilst still maintaining brake pressure, clutch out again. at this point you can still be on the brakes.
nomally when approaching a hairpin from a 4th gear straight i would brake - heel and toe into third - heel and toe into second - release brakes - turn in to corner.
rev matching is just making sure the engine speed matches the wheel speed of the new gear - this can simply be downshifting from 5th to 3rd for an overtake for example, one would blip the throttle whilst changing gear so as not to make the car lurch when you engage 3rd gear. with practice it doesnt even need a blip - say you're accelerating in 5th, but want to downshift to 3rd - once you dip the clutch the continued pressure on the throttle will make the revs rise, then you can just engage the lower gear when the revs are high enough.
double declutching is largely redundant on any modern car as all have syncromeshes on the gears - and can be done up or down the gears, whereas heel and toe is only used on downshifts.
and clutchless shifts are really only necessary if your clutch wont release - but its pretty straightforward, especially upshifts - just pull the stick out of gear, then as the revs drop, gentle pressure on the stick towards the next gear should see it slot in when the revs match. dont force it otherwise you'll get a horrible grinding noise! for downshifts a blip on the throttle is definitely required as above.
One way i like to think about driving is imagine a nearly full glass of water on the passenger seat - if anything you do causes the water to slosh around so mush it spills over, be it accelerating, braking or cornering, you're not driving smoothly.