To cast a spell is easy it is controlling when not to cast which can be the problem.
In short there are two parts of spell casting, imagining and intent,
How well you imagine controls everything, the more you actively visulise the stronger the spell.
If you can visulise and feel at the same time then you have a spell. But remember you should learn cicles of protection this helps shield unwanted entities out.
Please note the stronger at magic attacks more entities for good or bad.
Just remember defense first then what ever,
So what is spell casting