The actual "casting" of the spell, the part that sends the energy to do it's job, is the zenith of the ritual or ceremony when you are visualizing the desired act happening with your emotions high and you hold, or continue this until you feel within yourself that your spell is on it's way.
The ritual ceremony is a tool to help you get to the place where you send out the energy for the spell you are doing. Even before you begin the ceremony you begin to prepare with a cleansing of the body and mind. Then in your ceremony you wrok to build up your emotions and get your mind focused on the target and the goal (spell). Then you come to the place where you have all three together and you release it to do your work. Then you have a closing, or a winding down period.
It's best to design your own ceremonies but you can use other ones already designed if you wish. The whole process from the cleansing preparation to the close of the ceremony is the casting of the spell.
When doing any spell you always need these three things:
A clear focus on the target of your spell
A clear focus on the goal of the spell (healing, money, love, etc...)
High emotional level of an appropriate kind
When you can visualize clearly with high emotions you have successfully cast your spell.