Its sucks to say im a noob. This is my first stick shift car and now it is in the shop as some of you know what happened to my car and saw my post. But yea i only have 1500 miles of manual transmission in play, and i have no clue what you guys are talking about with the "heel toe" thingy.lol I knwo what your talking about with the rev matching when downshifting but im to afraid to try that i think i'll porb break my car or something. I wish i did not know how to do all that though sounds very interesting. Anyone live around the north jersey area that doesn't mind showing me all this shifting technique stuff it would be greatly appreciated. And hopefully i get my baby roxanne back soon, i miss her

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Edit: I was tired earlier today and got the heel and toe positions reversed. You'd have to have a double jointed ankle to do it the way I explained it. Sorry for the brain fart. Corrected now.
Heel and toe is where you rev match while braking (so downshifting while braking). It's done by angling your right foot so that the heel engages the accelerator pedal while the toe of the same shoe engages the brake pedal. You independently modulate the throttle with your heel to rev match the downshift. Braking is done with the toes.
Double clutching is also for downshifting and is when you release the clutch pedal twice during a downshift. The first time is when the transmission goes into neutral (as in a 3 > Neutral > 2 downshift). This spins up the gears and shafts in the gearbox so that everything is nicely in sync when shifting into 2nd. Final clutch release is when fully in 2nd. It looks like this for a 3rd gear to 2nd gear downshift:
Press clutch pedal in > shift from 3rd to Neutral > release clutch pedal and blip throttle to get revs slightly past point where gearbox would be if in 2nd at that speed > press clutch pedal in > shift from Neutral to 2nd > release clutch pedal.
Sounds complicated but with practice it becomes second nature. Real challenge is to combine heel and toe together with double clutching. This takes a lot of independent heel and toe motion along with clutch foot and right shift hand, usually while steering too (this should be done before entering corner but ...).
To answer the original question of this thread, I used to double clutch in some of my previous cars ('70s and '80s) but I haven't really practiced it in years. I do once in a while just for the heck of it, but I'm sloppy and out of practice.
Most modern transmissions with full synros are so good that with some attempt to rev match the shifting is smooth and effortless. As already explained in this and other threads, double clutching was a skill necessitated by early transmission designs without syncros. Downshifting without double clutching would put un-necessary stress on easily broken gearbox parts and/or disrupt the balance of the car as low engine revs exert an instant engine braking on the back tires (older cars with non-syncro gearboxes were typically RWD) possibly causing a spin (aggravated further by the toe changes in the antiquated rear suspension designs when weight shifted forwards due to mismatched downshift).