So a strip has a long edge and a short edge. You hold a short edge. You described the short edge not being held as getting snagged in wax.
What you should learn is to carefully fold in a bit of that sticky edge and then “top and tail” so you let go of the short edge you are holding and instead hold the strip at the other end that is all sticky. If you put your fingers on the folded over edge that stops you sticking to the wax.
You should be taught not to be wasteful on your course. If you need half a pack of strips per client and you have 8 clients a day, your employer will need 20 packs a week. That”s half a box. Boxes need space to store and ordering goods takes time, to order and unpack and put away, not to mention the cost. Waste also costs money to dispose of. A black bag is about £3 to get collected by waste collection services.
if you use too many strips you’ll also be using too much wax. Pulling off thick quantities of wax is potentially damaging for skin, some people have very sensitive or soft skin so you could damage their skin. Black skin is butter soft.
Professionals use expensive wax. Wax is very cheap - around £10 per kilo but professional high quality wax is more like £25 per kilo. It’s the same with strips. The good stuff costs double. I order wax from a specialist supplier once a month and I can’t store a whole van load! I need everyone to be frugal. Ultimately managing costs is about concern and care for the environment, your body (more product applied = more effort to remove), giving your client the most comfortable experience, and not charging your client more than you should need to (or bankrupting your boss). It’s also about not throwing your pay rise in the bin!
I took ages to perfect my waxing technique. In the end I put myself on Groupon. After 68 full leg waxes I’d found my groove, learned to do a full leg, underarm and bikini wax in 45 minutes without feeling knackered and learned to manage my costs. Stick at it!