Conferral is a principle of the EU which holds that the body can only act with authority that has been expressly provided for it through treaties. It is a principle that operates in a similar manner to federations such as the United States, Canada and Australia, whereby individual states confer authority to a central federal government According to the law of conferral, the EU is a body of member states meaning that the EU’s legal capacity and laws are decided upon by those member states. The EU does not have full jurisdiction by right, so it only has power over things which are explicitly outlined in its policy. Anything that has not been mentioned in EU law is strictly the matter of singular member states. It is explained in Articles 4  as well as 5 of the TEU.
The articles clarify that the EU acts only within limits of the power which the members have bestowed upon it. 4  states that those competences which are not conferred upon the EU by way of the Treaties remain with the Member [Countries].’
It goes on to say that each member state is equal, and the EU must respect their own national identities which are inherent in their history and fundamental structures such as government and constitutions, as well as the geographical territory of the member state.
Tridimas, T. (2007). The general principles of EC law (2nd ed.). Oxford: Oxford University Press.