What does "Creeps in this petty pace from day to day" mean?Please i only want an explenation for that line.

The line you ask about in Shakespeare's
Macbeth is from the famous "Tomorrow" speech, spoken by Macbeth. 
Here's the line with some context:

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She should have died hereafter [at some better
time; later, rather than sooner];

There would have been a
time for such a word [the word he just received that his wife was
dead].

Tomorrow, and tomorrow, and
tomorrow

Creeps in this petty pace from day to
day

To the last syllable of recorded
time,

And all our yesterdays have lighted
fools

The way to dusty death....  (Act
5.5.17-23)

The repetition of
tomorrow suggests tedium, endless repetition, and tomorrow creeps
in slowly from one day to the next, always, and it is just as useless as all of the
yesterdays.

Macbeth slips into nihilism, here, the belief
that nothing matters, and nothing makes any difference.  His wife's death is the trigger
that moves him to hopelessness.  All the yesterdays lead one only to the dusty grave. 
And between the beginning and the end what happens is
irrelevant.

Interestingly, this scene is one of several
that shows Macbeth figuratively jumping back and forth between emotionally feeling he is
invincible because of the witches' predictions, and rationally knowing the predictions
are too good to be true and that he is doomed.