Online videos can help you, if you already are a trained ballet dancer, to perform better and better. Keep in mind that ballet needs work and needs to be learned with a real teacher, and "on line lessons" will never avoid taking real ballet lessons, with a real teacher in a real school.
In any case, do not perform any work en pointe before you have been granted to dance en pointe by a professionnal ballet teacher. Otherwise, you may hurt yourself (in the worst case) or take very bad habits (in the best case), that may lean you to a poor en pointe performance.
Remember, before beeing an art, ballet is a very athletic sport, and as any sport, needs serious training.
Have a watch to this page about ballet learning ballet from YouTube ballet videos before performing any video work.
Learn Ballet the way it is taught at the Royal Academy of Dance in England (the well known RAD).
This video shows you how to perform a1st Port De Bras(A)
Those videos may be of interest, too ...

