You can practice on the grass. Kind of hard to explain in a post. Better-more expensive nets are easier to open..like maybe 80 bucks and up for a 6-8- radius net. Betts makes some decent nets. Stay away from store branded nets. That is what I have now beause it was the only thing available at the lake that day and I regret it every time I unroll it. Some videos and instructions show guys holding the net in their mouth. I've never found that necessary in nets up to 8'..never tried anything bigger.
Might be easier to learn with a smaller net. The better nets will lay flat on the ground when spread out. Cheap nets nets will have a big bulge in the middle when spread out on the ground. I don't know what kind of net you have and am in no way suggesting you spend money for another one. You can certainly learn with any net. I would suggest to trying to find some body to show you how they do it. Larger nets with more weight per foot (over a pound per foot of radius) seem to be harder to open for me or require a different technique. The better nets are made with pie shaped sections so they lie flat. I think I started with a 3 foot radius net (that's just what I was given) and moved up to 6 and 8 radius. I think in 15 minutes somebody that knows how could have you throwing it to get it one half to three quarters open which is enough to catch bait. Once you learn how to that then the quality of the net (and better technique) will make a difference. With shinners at $15 per pound it will pay off.
If you are throwing it in shallow water (2-8) with rocks, re-bar and trash on the bottom, like in a river, use a cheap net becaues it will get torn up or lost and that's worse than not opening.
Stick with it.