We used this book – Explaining Shirk by Sheikh Uthaymeen to explain in further details.
Any acts of worship that is other than Allah and the reward of worship is sought from the creation instead of the Creator falls under Shirk in Tawheed Uluhiyah or shirk in Tawheed of Eebadah.
It may fall under major shirk or minor shirk.
When any worship is directed to other than Allah. This is exactly what prophets were sent by Allah to call mankind away from
An Nahl 19: 36
And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): “Worship Allâh (Alone), and avoid (or keep away from) Tâghût (all false deities, etc. i.e. do not worship Tâghût besides Allâh).” Then of them were some whom Allâh guided and of them were some upon whom the straying was justified. So travel through the land and see what was the end of those who denied (the truth).
One of the meaning of taghuts is worshiping other than Allah.
A lot of emphasis has been placed on the evil of shirk in Eebadah because it contradicts the very purpose of our creation
Dhariyaat 51: 56
And I (Allâh) created not the jinn and mankind except that they should worship Me (Alone). (56)
Major shirk of this kind is an act of rebellion against the Lord of the Universe, and thus it is an ultimate sin. It is a sin so great that it virtually cancels out the good deeds and the place is hell (if he does not repent before he dies).
False religion is also based on this shirk. False religion will ask its followers to worshup the creation and not the creator
i. Christians call to worship a man – Prophet of God Jesus alalihi salam.
ii. Catholics pray to Mary the Mother of God.
iii. They also worship angels like Michael who is honoured on the 8th May and 29th September. there is also Michaelmas day as St. Michael as well as human saints
iv. There are Muslims who fall in this class who make du’a t Prophet muhammad sallallahu alaihi wasalam or mystics saints.
Mahmood ibn Lubayd reported that Allaah’s Messenger (peace be upon him) said,
“What I fear most for you is minor shirk (ash-shirk al-Asghar)”
The companions asked, “O Messenger of Allaah! What is minor shirk?”
He replied, “Ar-Riyaa, for verily on the Day of Resurrection when people are receiving their rewards Allaah will say:
‘Go to those whose admiration you sought in the world and see if you can find any reward from them.’”
Collected by Ahmad, at-Tabaraanee and al-Bayhaqee and authenticated in Silsilah al-Ahaadeeth as-Saheehah, vol.2, p.671, no.951.
Mahmood ibn Lubayd also said,
“ The Prophet (sallaALLAHU alaihiwasallam) came out and announced, ‘O people, beware of secret shirk!’ The people asked, ‘O Messenger of Allaah, what is secret shirk?’ He replied, ‘When a man gets up to pray and strives to beautify his prayer because people are looking at him, that is secret shirk.’”-Collected by Ibn Khuzaymah