What are "Secret" spells:
Secret spells are that spells, which are not taught in class. Some wizards and witches in Hogwarts learned them, figured them out and shared them with their friends. It is said, that, once you learned a spell from a friend, you shall share it, but only two one - three persons, otherwise Peeves comes over you
In the following you see, how to learn these spells:
1. Never dm the Owner or Co-Owners to tell you a spell and their movements!
2. Make friends
3. ask your FRIEND, not some random person
4. If you are shy and just want to learn some spells, but don't want to make friends, just stay around some people, but don't stalk... maybe you can figure out some movements or icantations.
5. Once you got an idea of the spell movements, you ca try out. If you didn't get the movements right, try some variations
It is not forbidden to copy the wand movements from someone, who was so "clever" to practice that spell at a public place! So don't complain if Ron starts to practice Confringo, right after Hermoine started to practice it at Hagrid's hut.