Shirk (a.k.a Shituff)is a very broad concept in Islam, unlike Judaism and is the antithesis of Monotheism (Tauhid), an equally broad subject.
Shirk is viewed in Islam as a violation of Allah's right in the sense that to Allah alone belongs all worship, following and love in a manner it befits his majesty(not how you love your parents , wife etc).
Infact Allah terms the person who commits Shirk as the greatest oppressor as he is trampling the fundamental rights of Allah :
“Indeed shirk is the greatest oppression.” [Quran,Luqman: 13]
And hence is the single biggest Sin in Islam to the extent there is no forgiveness for the person who commits it and dies without repenting.
"Verily, Allaah forgives not that partners should be set up with him in worship, but He forgives except that (anything else) to whom He pleases, and whoever sets up partners with Allaah in worship, he has indeed invented a tremendous sin." (Nisaa, 4:48)
Shirk can be done with the heart, tongue and limbs,Shirk in itself can be divided into three types:
- Shirk ul-Akbar (The major shirk) (Includes Idolatry)
- Shirk ul-Asghar (The small shirk) (Includes Hypocrisy)
- Shirk ul-Khafie (The hidden shirk) ( Inconspicious Shirk )
Shirk ul-Akbar (The major shirk)
Idolatry is classified as a Major Shirk in Islam. Regarding your question on difference between Avoodah Zara(Idolatry) and Shituff(Shirk) than Idolatry means that you are associating an Idol in worship instead of worshipping Allah alone , Hence Idolatry is a type of Shirk(Association). In Islam the major Shirk takes one outside the fold of Islaam(becomes a Kafir\disbeliever), whereas the minor Shirk does not, though it can lead to major shirk.
"They have become kaafir those who say: 'Verily Allaah is al-Maseeh (Jesus) the son of Maryam (Mary)…" (Maaidah, 5:17)
You can avoid committing Shirk by studying the Islamic Shariah(Islamic counterpart of Halaka); by doing so, you will know not to do them for anyone other than Allaah, such as prayer, fasting, da’wah, slaughtering etc
Some more examples of Shirk ul-Akbar:
Shirk ud-Du'aa (The Shirk of Invocation).
This type of shirk implies invoking, supplicating or praying to others
besides Allaah Almighty, such as to supplicate to a dead person in his
grave etc. This form of shirk is widely common in parts of Indo
Subcontinent and among some Sufis.
Shirk ut-Taa'ah (The Shirk of Obedience)
This type of major shirk implies obeying any authority or law other
than the Sharee'ah (obeying the commands of other than Allaah). If you
obey any law other than Allaah it is considered to be Shirk at-Taa'ah,
Allaah Almighty says:"They (Jews and Christians) took their rabbis and their monks to be their lords besides Allaah (by obeying them in
things which they made legal or illegal)..." (Tawbah 9:31)
Once, while Allaah's Messenger (Peace be upon him) was reciting the above verse, 'Adee bin Haatim said: 'Oh Allaah's Prophet! They do not
worship them (i.e. their Rabbis and Monks).' Allaah's Messenger (Peace
be upon him) replied: "Did they not obey them (the rabbis and monks)
when they allowed what Allah made illegal, and forbid what Allah made
legal? 'Adee bin Haatim replied: 'Yes'. Allaah's Messenger (Peace be
upon him) said: 'This is their worship (of them) '" (Tafseer
al-Qur'aan al-'Azeem of at-Tawbah verse 31)
Shirk ul-Mahabbah (Shirk of Love)
This type of shirk involves loving those who Allaah hates (i.e. the
Kafirs) or hating those who Allaah loves (i.e. the believers). Allaah
"And of mankind are some who take (for worship) others besides Allaah
as rivals (to Allaah). They love them as they love Allaah. But those
who believe, love Allaah more (than anything else)..." (Baqarah,
There are many other forms of major shirk which are detailed in the
magnum opus and revolutionary book o Kitaab ut-Tawheed (The Book of
Tawheed) by Sheikh Muhammad bin 'Abd al-Wahhaab (may Allah's
mercy be upon him).
Shirk ul-Asghar(The minor Shirk) -Ar-Riyaa' (showing off).
Ar-Riyaa' is any action which is performed in order to receive praise,
fame or any other worldly gain. It is a form of shirk, for rather than
doing your actions for the sake of Allaah you begin doing them for the
sake of yourself or others.
It is narrated in the Musnad of Imaam Ahmad and at-Tabaraani that the Messenger Muhammad (Peace be upon him) said: "The thing I fear most
for you is ash-Shirk ul-Asghar (The Small Shirk). The Sahaabah then
asked him: 'What is The Small Shirk?' He (Peace be upon him) replied:
ar-Riyaa (showing off)."
A person must never show-off with any of his prayers, da'wah or good
deeds etc. Any actions that are done out of showing-off will never be
rewarded as they were done for your sake, and not for Allaah Almighty.
Ash-Shirk ul-Khafie (The Hidden Shirk)
The Hidden Shirk can either be major or minor shirk, depending on the
area in which it was committed. Hidden Shirk is one of the most
dangerous forms of shirk as people cannot see that they are committing
it. It is committed unknwowingly.
Compiled from here , here and here