The problem with videos is that they do not give you an idea on how much pressure you really need to put on the animal.

In the majority of people that try to sex their animal for the first time, they either do not place their fingers properly (either too far or to close) and do not apply enough pressure.

Best is to have someone show you in person and after that it's about practice.

I have tough a few people over the years including my vet.