Cueing A Horse For The Stop & Back Up

I just bought a big 5yrs old 16hh paint, 2 weeks ago an the lady I bought her from said she'd rode her a couple times, but she been mainly put out to pasture for about a year. Well a couple days after I got her I saddled her an she done fine, I hopped on her an she walked good she didn't seems to like that bit , so a couple days later I bought her a snaffle bit an saddled her up again the bit seemed to make all the differents she walk ok, but when I tapped her flanks to get her to a trot that when she came unglued bucking, she bucked me off, well I walked up to her an got right back on an we walk up to the barn cause I was done. Can u please give me some pointers an on what I need to do.
Thanks. Shane Jones

Thanks Larry, have had a vast improvement on my stops since watching this video and practising what you showed

My question: Is the horse in this video wearing sliding plates? Or is that a stop we can expect out of an unshod or plainshod horse? And is asking them to stop that strongly all the time hard on the joints? Of course I understand that footing will play a major factor as well… The filly my video is a pretty well bred Nu Chex to Cash filly who is very capable and has a nice stop when I ask for it but my trainer has warned me it may not be good for her. While she is reining and cowhorse bred, we actually do contest riding primarily – barrel racing and gymkhana – so we don't know a lot about training the reining horse. I just thought they looked fun to ride so I bought one! She's just coming 4 and was started at 3 and is primarily trained by myself – a rank amateur. She's unshod and I prefer to keep my running horses that way. Should I still expect a Nu Chex To Cash quality stop (she can do it) or should a stop her more like a hunter horse to protect her soundness….? Thanks for this great forum!