I am sure there is a spell, article, or even forum thread which would explain shielding of you searched for it. Google would also have a plethora of answers. I recommend doing some research as there are various methods to shield, and my way might not be your way.
The basic foundation on Magik is energy work. You need to grasp this before you can cast spells. Charge Magikal energy into your body. Ground Magikal energy out of your body. Shield your body with Magikal energy to protect yourself. Once you have grounded the negative energy from your body and charged your body with positive energy, you should shield. Shielding protects you from other Witches casting on you, which is not common, but still possible. More importantly, it keeps the negative energy of daily life from clinging to you and bringing your energy down. It is far more common to come across someone in a foul mood who unwittingly sends negativity your way than a Witch casting on you.
Focus on your center. Where this is varies, but where you feel your center of gravity is would be your center. People typically think of their stomach, or solar plexus, but there is no wrong answer except for what does not resonate with you. Feel the positive energy pooling in your center and creating a ball of shimmering light. Let this ball expand and surround you. If you wish to think of something from a movie, like Glinda's pink orb, Avatar Aang surrounded by the elements, or Kida from Atlantis after she has become one with their energy source those all work. Same with any type of protection you can imagine. The point is to surround yourself with this energy and feel safe. When you are new, you might have to do this throughout your day, but with practice, you can do it once and be set.
https://www.spellsofmagic.com/read_post.html?post=829288 That should help you. Also, go to the site forums and click on the General Info section. There are a number of helpful forums pinned at the top.