Question: A foreign friend of mine has just become a Muslim. What should we teach him before all else? 
ANSWER
First of all, you must teach him iman; that is, you must teach him Allahu ta’ala, His Attributes, Hadrat Muhammad’s being His Prophet, the six pillars of faith, and then the five fundamentals of Islam. After teaching the foregoing, you should help him perform salat because it is stated in a hadith-i sharif:

(When you are sent on a mission to a tribe whose people are Ahl-i Kitab [the people of the Book], firstly invite them to say “La ilaha ill-Allah Muhammadun Rasul-Allah.” If they accept your invitation, notify them that it is fard to perform salat five times a day. If they also accept this, tell them Allah has made zakat fard, which is taken from the rich and given to the poor.) [Bukhari, Muslim, Abu Dawud]

In the above-mentioned hadith-i sharif, belief in Allah as well as confirmation of His Prophet takes priority over others. A person who does not confirm the Prophet of Allah is not a Mu’min or Muslim.

Question: Is it necessary for a person who has just become a Muslim or for a child who has reached the age of discretion and puberty to say the Kalima-i shahadat first, to learn its meaning, and to believe in it?
ANSWER
Yes, it is necessary. Afterwards, they have to learn and believe in the creed written in the books of Ahl as-Sunnat scholars.

Following this, they have to learn rules pertaining to practices from the books of any of the four righteous madhhabs; that is, they have to learn and believe in the five fundamentals of Islam and halal [permitted] and haram [prohibited] things and lead a life accordingly. If one does not believe that it is necessary to learn and to live up to them and if one does not consider them important, one becomes a renegade. In other words, after becoming a Muslim by saying the Kalima-i shahadat, one becomes a disbeliever yet again.

If a Muslim girl with nikah [marriage contract as prescribed by Islam] does not know Islam when she reaches puberty, her nikah becomes void [she becomes a renegade]. The Attributes of Allahu ta’ala must be told to her, and she must repeat them and say, ‘‘I believe in them.” (Durr-ul-mukhtar)

In explaining this, Hadrat Ibni ‘Abidin states:
If the girl is little, she belongs in her parents’ faith; she is a Muslim. When she reaches puberty, she does not belong to her parents’ faith any longer. If she reaches puberty being unaware of Islam, she becomes a renegade. Even if (s)he who has heard of the creed of Islam but has not believed in it utters the Kalimat at-tawhid (La ilaha ill-Allah Muhammadun Rasul-Allah), (s)he is not ruled to be Muslim. A person who believes the six pillars expressed in “Amantu billahi ...” and who says ‘‘I accept the commandments and prohibitions of Allahu ta’ala” is a Muslim. Muslims must do their best to get their children to memorize the Amantu and must teach them its meaning precisely. If children do not learn the six pillars of belief and do not utter their faith in them, they are not Muslims, but renegades, when they reach puberty.

It does not suffice to say “I believe in Allah.” One who has denied any of the six pillars of belief, e.g. faith in qadar, becomes a disbeliever, and all of one’s good deeds perish. (Radd-ul-mukhtar)

Question: If a disbeliever says, “Bury me in accordance with the rules of Islam,” can we consider that person a Muslim?
ANSWER
No, you cannot. If that person says the Kalima-i shahadat or its meaning, then you can.

Question: I have just become a Muslim. I do not have enough knowledge of religious practices. I am learning everything from scratch. Therefore, I do not know in detail acts and statements that cause disbelief. If I unknowingly say or do something that is a sign of disbelief, what will be then? If I do it without knowing, will I lose my iman [belief]?
ANSWER
No, you do not lose your iman. A person who has become a Muslim in such a country as Poland cannot know all things that cause disbelief. As that person cannot know all things, we should not say, “You have become a disbeliever.” What to do then? It will be enough to say: “I believe Allahu ta’ala and His Messenger, and I believe, love and accept all the messages he (the Prophet ‘alaihissalam’) brought from Allahu ta’ala. I love the friends of Allahu ta’ala and of His Messenger, and I hate their enemies.” A person who feels uncertain about something conveyed by our religion must say, “I believe whatever Allahu ta’ala and His Messenger mean by this.”

Importance of sajdah
Question: If a non-Muslim performs sajda-i tilawah after listening to an ayah requiring sajda, is he/she ruled to be a Muslim?
ANSWER
Yes, it can be inferred that he/she has converted to Islam. (Bazzaziyya, Ibn Abidin)

Likewise, a person who performs salats in jama’at is ruled to be a Muslim because salats in the religions before Islam used to be performed individually, not in jama’at. (Islam Ahlakı)

In our religion, as the ruling is according to what is apparent, when a non-Muslim does above-mentioned acts of worship, they are ruled to be a Muslim. However, unless they desert their false religion and unless they believe in what our religion states, they are not in reality Muslim just because they do these acts of worship. Maybe they are a hypocrite in their heart who show themselves a Muslim in public. However, they are treated as a Muslim in worldly life unless they display a deed or word that reveals disbelief (kufr).

Question: For a person who has converted to Islam in a non-Muslim country, is it necessary to perform fards and abstain from harams immediately?
ANSWER
One who converts to Islam in a non-Muslim country has to obey fards and abstain from harams when one hears of them. However, one who converts to Islam or one who has reached puberty in a country where Muslims live has to perform fards and abstain from harams immediately. Likewise, one who has become Muslim in a country where Muslims live has to make qada of those salats and fasts that one did not perform until one heard of them. Not knowing them is an excuse that saves one from the sin of omitting them. If one knowingly neglects to learn them, then there is no excuse for one.

Question: What is the first thing that every Muslim, man or woman, has to know and believe?
ANSWER
Every Muslim, man or woman, who has reached puberty and sanity has to know Allah. That is, he/she has to know the attributes (Sifat adh-Dhatiyya and Sifat ath-Thubutiyya) of Allahu ta’ala correctly and believe in them. This is the first fard on everyone. Not knowing them is not an excuse, but a sin.

Question: Does a person who has just converted to Islam perform ghusl?
ANSWER
When a non-Muslim converts to Islam, it is mustahab for them to perform ghusl.

Note: There is detailed information about the six pillars of faith in the other articles.