Can someone please give a brief answer describing the major and main responsibilities which is a must and sufficient enough to make a Muslim.
Please provide references as well.
A person who just believes in
Is called a believer. In Arabic and in Quran the word Momin is used for them which means/translates to believer.
On the other hand, a Muslim is a Momin/believer who observes and practically follows Islam, mainly following Pillars of Islam
I am taking literal meanings of momin and Muslim.
Muslim is, say, of higher rank than Momin. Once a momin (faithful) starts following Islam practically, he is a Muslim (obedient).
Once a Muslim stops practicing Islam, he is a momin. He (that specific person who stops practicing Islam because of laziness) may be called a hypocrite (minor hypocrite).
There are two types of hypocrites.
The Muslim is the person who has accepted Islam as his/her religion and prophet Muhammad (pbuh) as the Prophet of Islam. A real Muslim ought to say Shahadatain(2Shahadahs). As well as this, a Muslim ought to perform the orders of Islam.
There is a tradition from Prophet Muhammad (Pbuh) that said:
The Muslim is a person that other Muslims must be comfortable from his hands and tongue.
Imam Ali (a.s.) divided the Islam(Muslim) into six steps:
Islam is submitting against the right and submitting is not possible without Yaqin(certainty) and the certainty is validity and the validity is confession (it means it is not sufficient that Islam and faith(Iman) stays in heart and spirit of human, haply ought to express it with dare and power) and confession for doing the duty and doing the duty is performing the orders of Allah.
On the other hand, according to Shia, there are five Osul al Din or 5 principles (Articles) of the religion or faith which a Muslim must believe in them and they consist of:
1: Tawhid (oneness)
2: Adalah (justice)
3: Nubuwwah (prophet-hood)
4: Imamah (leadership)
5: yawm al Qiyyamah ( the day of resurrection)
And likewise In accordance with Shia, the ten Ancillaries of the Faith (furūʿ ad-dīn) (فروع الدين} have practices that a Muslim must perform:
1 Salāt (Prayer)
2 Sawm (Fast)
3 Hajj (Pilgrimage)
4 Zakāh (Charity)
5 Khums (One-fifth)
6 Jihād (Struggle)
7 Amr-Bil-Ma'rūf (Commanding what is good)
8 Nahi-Anil-Munkar (Forbid what is evil)
9 Tawalla (Expressing love towards Good )
10 Tabarra (Expressing disassociation from Evil)
From this question "What is difference between Islam and Iman?" we can extract your answer...
He then asked the Prophet "What is Islam"?
The Prophet replied:
"Islam is to worship Allah and not do shirk, to establish prayers (salat), to pay charity (zakat), to fast (sawm) during the month of Ramadan, and hajj to the house." [Sahihayn & Sunan]
A person who does the above things is a 'Muslim'(Person who does or follow 'Islam' - Submit to Allah).
May the creator guide us all.