Eissy is quite correct.A spell is much more spiritual than physical. Aspell is a "ritual wish",like a prayer.The difference is that a prayer is asking for help from a highre authority.A spell is a do-it-yourself operation.Personally, I don't cast spells,but from what I understand the main changes from a spell are very often in the person casting the spell.
Perhaps you are thinking too much of a spell being "magic".That's not strictly true. You have to sincerely believe in a spell,magic can be demonstrated.It is all around you in nature.Physical magic is changing one thing for another. For instance, if you keep some seeds in a jar or box,nothing will happen. But if you add good soil,water, and sunshine,the magic happens!
Not all witches,not even all Wiccans, cast spells.But they may still have their beliefs in the spiritual side.