You cannot simply try to cast a spell without a great deal of study.
You first have to understand what a spell is! A spell is a ritual "wish".Very like a prayer.The difference being that with a prayer you are "asking" for help from a higher Being, or Deity. A spell is a "do it yourself" prayer. A spell is using your own energy with that of the enormous energy of the Earth, to make changes in yourself and/or your environment. You have probably cast very simple spells in your life without being aware of it! If you have ever blown out the candles on a cake and made a wish, you have cast a spell. Ever pulled a wishbone? That's another spell.
But really serious spells are very serious indeed, and not to be played about with! For a spell to work you need to be connected with the Earth (Grounding). You need to cast a protective circle, so that no negative influences can interrupt your spell. You need to be "centred". You need to first meditate, and then visualise what you want your spell to achieve. For this you need to study; a lot!