Typically there are two types of NDA’s, a unilateral or one sided agreement and a mutual agreement.
Most NDA’s are one sided and used by the inventor to protect themselves from any information that is disclosed to another party.
Im sure you could guess this one. A mutual NDA is written to protect both parties who need to disclose information to each other. This mutual NDA is typically used when 2 parties are looking to merge or form a joint venture.