What is al-Salafia and is true belief in Islam?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

al-Salafiyah means following the good predecessors in their faith, actions and words. The word 'al-Salaf' refers to the companions of the Prophet (Sallallahu Alaihi wa Sallam), their immediate followers and those who follow the followers of 'Sahabah'. The basis for this explanation is that the Prophet (Sallallahu Alaihi wa Sallam) particularly distinguishes with goodness of his generation and the two generation after it. He (Sallallahu Alaihi wa Sallam) said: "The best people are those living in my generation, then those coming after them, and then those coming after them (the second generation)" . Imran the reporter of the Hadith said: 'I do not know whether the Prophet (Sallallahu Alaihi wa Sallam) mentioned two or three generations after his generation'. Then the Prophet (Sallallahu Alaihi wa Sallam) added, "There will be some people after you, who will be dishonest and will not be trustworthy and will give witness without being asked to give witness, and will vow but will not fulfill their vows, and fatness will appear among them" . [Reported by Imams al-Bukhari and Muslim ].
Allah Says (interpretation of meaning): {You [true believers in Islâmic Monotheism, and real followers of Prophet Muhammadand his Sunnah (legal ways, etc.)] are the best of peoples ever raised up for mankind; …} [3:110].
Imam al-Zahhak said: 'The Salaf are the Prophet's (Sallallahu Alaihi wa Sallam) companions and the callers towards Islam whom Muslims are ordered to follow them'. The followers of those would be considered al-Firqah al-Najiyah (the saved group), Insha Allah. Because Allah has justified the Prophet's (Sallallahu Alaihi wa Sallam) companions (Radiya Allahu Anhum).
To merely affiliate with 'al-Salaf', or to adopt a certain surname like 'al-Salafiyah' or 'al-Salaf' or similar names is not sufficient. Basically, there is a principle which states the realities are taken into account not the names by which things are described. The criterion is following the Qur'an and Hadith.
Allah knows best.