@ We_Eat_Cake to assume it was in regards to your spell, it might just mean the spell was cast, perhaps you used too much energy if it wasn't a weather spell. it isn't a bad thing, magic is energy, it's neither good nor bad, only the caster can determine if the spell is good or bad.
aliayyam you will know you're a good spell caster simply by intent. if you wish to do 'white magic' and cast for good, then that's how you'll know. if you mean how to know a spell was successful, harder to say. spells can take anywhere from minutes to months to work, with practice you'll become stronger at your skill and it will take less time [unless the spell specifies on the length it'll take]