“Recognition” and “United Nations membership” are often used as if they mean the same thing. Under international practice and the UN’s own explanation, they are different processes.
Recognition is an act by individual states and governments. A government may decide that it recognises another entity as a state and may establish diplomatic relations with it. Other governments can make a different decision.
The United Nations itself does not “recognise” states in that diplomatic sense. The UN explains that, because it is an organisation rather than a state or government, it does not possess authority to grant or withhold diplomatic recognition.
UN membership is instead governed by the UN Charter. Article 4 says membership is open to peace-loving states that accept the Charter’s obligations and are judged able and willing to carry them out.
Admission requires two institutional steps. First, the Security Council must recommend admission. Then the General Assembly decides whether to admit the applicant.
That distinction produces situations that can look confusing. An entity can be recognised as a state by many countries without being a full UN member. Conversely, UN membership is powerful evidence of broad international acceptance but does not force every individual government to establish diplomatic relations.
There is also a separate question of representation. The UN may have to decide which representatives are entitled to occupy a country’s seat when rival authorities claim to be the government. That credentials issue is different again from recognising whether the state itself exists.
For readers, the useful three-part framework is: recognition asks what individual states accept diplomatically; UN membership asks whether the organisation admits an applicant under the Charter; credentials ask who represents an existing member at the UN.