Tawhid means that God is one.
There is nothing like God. He is the
one and only supreme power and is
beyond human understanding.
He is The Supreme, The One.
Allah is The Eternal and The
Absolute. None is born of Him
and He is The Unborn. There is
none like unto Him. (Surah 112)
No vision can grasp Him; but His grasp is
all over vision. He is above all
comprehension, yet He is acquainted
with all things. (Surah 6:103)
Shirk is the opposite of
Tawhid. It is to disobey
God and not follow his
rules.
Examples of Shirk: imagining God is like a human
being or any created thing, thereby making Him
limited and less impressive than He is; thinking we
can comprehend what God is like; putting your own
ambitions on a level with God, or treating them as
more important;
Examples of Shirk:
worshipping anything, or
treating anything as
important as God, e.g. idols or
images of prophets or
superstitious beliefs