Core beliefs are beliefs about ourselves, other people and the world we live in. They are things that we hold to be absolute truths deep down. Essentially core beliefs determine how you perceive and interpret the world around you.
Many of us have unhelpful subconscious core beliefs that are driving our life choices. For example: If you are looking for love (and we all are), but your core belief is that you are unlovable this will create problems in your choices. When you meet someone who treats you with love and respect you are likely to reject them. You will believe something is wrong with them. They don’t really love and know you if they think you are worthy of this wonderful treatment. So you will not pursue the relationship.
Counseling, cognitive behavioral therapy, and self-inquiry are all good ways to sort out what your subconscious beliefs are. Once these beliefs are in your conscious mind you can begin to dispute and change them. Therefore changing the live decisions your make.